LIBRARY 


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BRIEF  INTRODUCTION 


TO 


QUALITATIVE  ANALYSIS 


FOR   USE 


IN  INSTRUCTION  IN  CHEMICAL  LABORATORIES. 


BY 

LUDWIG  MEDICUS, 

PROFESSOR   OP    CHEMISTRY    IN    THE    UNIVERSITY    AT    WtRZBURG. 


TRANSLATED  FROM  THE  FOURTH  AND  FIFTH  GERMAN  EDITIONS, 
WITH  ADDITIONS, 


BY 


JOHN  MAKSHALL, 


ASSISTANT   PROFESSOR   OF    CHEMISTRY    IN    THE    MEDICAL   DEPARTMENT 
OF   THE    UNIVERSITY   OF    PENNSYLVANIA. 


PHILADELPHIA: 
PEINTED   BY  J.  B.  LIPPINCOTT  COMPANY. 

1892. 


Copyright,  1891,  by  JOHN  MARSHALL. 


TRANSLATOR'S  PREFACE. 


THE  merit  of  Medicus'  "Qualitative  Analysis/'  and  its 
popularity,  which  is  shown  by  its  having  already  passed 
through  five  editions  in  the  German  language,  led  to  this 
translation. 

The  translator  has  taken  the  liberty  of  rearranging  the 
elements  in  the  first  part  of  the  book  into  groups,  to  corre- 
spond with  their  precipitation  by  group  reagents,  and  also 
of  adding  two  tables  and  amplifying  the  text  to  the  extent 
of  about  forty  pages. 

J.  M. 
PHILADELPHIA,  1892. 


237409 


CONTENTS. 


PAGE 

INTRODUCTION 7 

I. — PROPERTIES  or  THE  BASES     9 

I.  Group :  Silver,  Mercurous  Salts,  and  Lead 9 

II.  Group :     Mercuric    Salts,     Copper,     Bismuth,     Cadmium, 

Arsenic,  Antimony,  Tin,  Gold,  and  Platinum 15 

III.  Group :  Iron,  Chromium,  Aluminium      38 

IV.  Group :  Manganese,  Zinc,  Nickel,  and  Cobalt 44 

V.  Group :  Barium,  Strontium,  and  Calcium 50 

VI.  Magnesium,  Potassium,  Sodium,  Ammonium,  and  Lithium   53 

II. — PROPERTIES  OF  THE  ACIDS 59 

I.  Group :  Sulphuric  Acid,  Hydrofluosilicic  Acid 59 

II.  Group :  Sulphurous  Acid,  Hyposulphurous  Acid,  Phos- 
phoric Acid,  Boric  Acid,  Hydrofluoric  Acid,  Carbonic 
Acid,  Silicic  Acid,  Chromic  Acid,  Arsenic  Acid,  Arseni- 
ous  Acid 61 

III.  Group:  Hydrochloric  Acid,  Hydrobromic  Acid,  Hydriodic 

Acid,  Hydrocyanic  Acid,  Hydroferrocyanic  Acid,  Hydro- 
ferricyanic  Acid,  Sulphydric  Acid,  Nitrous  Acid,  Hypo- 
chlorous  Acid 73 

IV.  Group :  Nitric  Acid,  Chloric  Acid 84 

Appendix :  Acetic  Acid,  Oxalic  Acid,  Tartaric  Acid    ...    86 

III. — PRELIMINARY  EXAMINATION 90 

(a)  Preliminary  Tests  in  the  Dry  Way 90 

1.  Examination  in  the  Seduction-Tube 90 

2.  Examination  on  Charcoal 93 

3.  Examination  by  means  of  Microcosmic  Salt 97 

4.  Examination  in  the  Flame .  98 

(6)  Preliminary  Tests  for  Acids 99 

1*  5 


6 

PAGE 

IV. — SOLUTION  AND  FUSION 103 

1.  Dissolving  Oxides  and  Salts 104 

2.  Dissolving  Metals  and  Alloys 110 

3.  Sulphides  of  the  Heavy  Metals Ill 

4.  Cyanides Ill 

5.  Silicates 113 

Y. — DETECTION  OF  THE  BASES  IN  THE  WET  WAY 116 

Precipitation  of  the  Different  Groups 117 

First  Group 120 

Second  Group 123 

Third  Group 125 

Fourth  Group 127 

Fifth  Group 127 

Sixth  Group 128 

Separation  of  the  Bases  contained  in  the  Group  Precipitates  .  128 

Separation  of  the  First  Group 129 

Separation  of  the  Second  Group 130 

Separation  of  the  Third  Group 139 

Separation  of  the  Fourth  Group 146 

Separation  of  the  Fifth  Group 148 

Separation  of  the  Sixth  Group 152 

VI. — EXAMINATION  FOR  ACIDS 158 

VII. — APPENDIX.     Behavior  of  the  Compounds  of  the  Rare  Ele- 
ments     171 

Examples  for  Practice  in  Testing  for  the  Rare  Elements  ....    176 


INTRODUCTION. 


QUALITATIVE  analysis  treats  of  the  methods  of  ascertain- 
ing the  composition  of  substances  and  the  manner  in  which 
their  constituents  may  be  separated. 

Qualitative  analysis  determines  what  bodies  are  present, 
but  does  not  refer  to  their  quantity.  The  latter  is  the  object 
of  quantitative  analysis. 

The  following  pages  contain  a  systematic  course  for  the 
detection  of  bases  and  acids,  with  the  requisite  preliminary 
tests,  preceded  by  a  brief  description  of  the  behavior  of  the 
more  important  bases  and  acids.  The  behavior  of  the  rare 
elements  is  briefly  considered  and  explained  by  examples  in 
the  Appendix. 


I.  PROPERTIES  OF  THE  BASES. 


FIRST   GROUP. 

METALS  precipitated  as  chlorides  by  HC1,  hydrochloric 
acid :  Silver,  Mercurous  Salts,  and  Lead, 

SILVER,   Ag  (ARGENTUM). 
Atomic  weight,  1O7.66;   valence,  I. 

White,  glittering  metal ;  specific  gravity,  10.57 ;  melting- 
point,  954°  C. 

AgNOft  argentic  nitrate,  may  be  employed  in  making  the  tests. 

1.  HC1,  hydrochloric  acid,  or  a  soluble  chloride  precipitates 
white,  curdy  AgCl,  argentic  chloride.  At  first  the  liquid 
becomes  milky  in  appearance,  due  to  the  finely-divided  par- 
ticles of  precipitate  in  suspension,  but  on  shaking  or  heating 
the  liquid  the  precipitate  collects  in  curdy  masses  and  the 
liquid  becomes  clear. 

On  exposure  to  sunlight  the  precipitate  turns  violet  and 
finally  black,  due  to  the  liberation  of  a  slight  quantity  of 
chlorine.  The  precipitate  is  insoluble  in  HNO3,  nitric  acid, 
but  dissolves  on  agitation  in  NH4OH,  ammonium  hydroxide, 
with  the  formation  of  argent-ammonium  chloride : 
AgCl  +  NH4OH  =  AgNH3Cl  +  H2O, 

from  which  solution  it  may  be  reprecipitated  by  the  addition 
of  nitric  acid  : 

AgNH3Cl  +  HNO3  =  AgCl  +  NH4NO3. 
It  is  also   dissolved    by  KCN,  potassium  cyanide,  and,   in 

9 


10 

the  absence  of  free  acid,  by  Na2S2O3,  sodium  hyposulphite 
(thiosulphite). 

2.  NaOH,  sodium  hydroxide,  as  well  as  KOH,  potassium 
hydroxide,  precipitates  brownish-gray  Ag2O,  argentic  oxide, 
insoluble  in  excess  of  either  reagent. 

3.  NH4OH,  ammonium  hydroxide,  added  in  small  quan- 
tity, precipitates  brownish-gray  Ag2O,  argentic  oxide,  readily 
soluble  in  excess  of  the  reagent,  forming  AgNH3OH,  argent- 
ammonium  hydroxide : 

Ag20  +  2NH4OH  =  2AgNH3OH  +  H2O. 

4.  H2S,  hydrogen  sulphide,  precipitates  black  Ag2S,  argen- 
tic sulphide,  insoluble  in  dilute  acids  and  in  (NH4)2S,  ammo- 
nium sulphide.     Boiling  nitric  acid  dissolves  it,   with  the 
formation  of  AgNO3,  argentic  nitrate. 

5.  (NH4)2S,  ammonium  sulphide,  precipitates  black  Ag2S, 
argentic  sulphide,  insoluble  in  dilute  acids. 

6.  K2CrO4,  potassium  chromate,  produces  a  purplish-red 
precipitate  of  Ag2CrO4,  argentic  chromate,  soluble  in   am- 
monium hydroxide  and  in  nitric  acid. 

7.  Na2HPO4,    sodium    hydrogen    phosphate,   precipitates 
yellowish,  flocculent  Ag3PO4,  argentic  phosphate,  soluble  in 
ammonium  hydroxide  and  in  nitric  acid. 

8.  KI,  potassium  iodide,  precipitates  yellowish,  curdy  Agl, 
argentic  iodide,  insoluble  in  dilute  nitric  acid,  and  almost 
insoluble  in  ammonium  hydroxide. 

9.  KCN,    potassium    cyanide,    precipitates    white,    curdy 
AgCN,  argentic  cyanide,  soluble  in  excess  of  the   reagent 
and  in  ammonium  hydroxide,  insoluble  in  dilute  nitric  acid. 

10.  Compounds  of  silver  fused  with  Na2CO3,  sodium  car- 
bonate, in  the  reducing  blowpipe  flame  on  charcoal  yield  a 
white,  ductile  globule  of  metallic  silver,  usually  without  an 
incrustation.     Occasionally  a  slight  reddish-brown  incrusta- 
tion of  oxide  is  produced. 


11 


MERCURY,   Hg  (HYDRARGYRUM). 
Atomic  weight,  199.8;    valence,  II. 

Silver-white  metal  ;  specific  gravity,  13.59  ;  solidifies  at 
—39.4°  C.  and  boils  at  357.2°  C. 

Mercury  forms  two  series  of  compounds,  named  respec- 
tively mercurous  and  mercuric  compounds.  Hg2O,  mercu- 
rous  oxide,  may  be  taken  as  the  type  of  the  mercurous,  and 
HgO,  mercuric  oxide,  as  the  type  of  the  mercuric  compounds. 

BEHAVIOR   OF   MERCURY   IN   THE   MERCUROUS  CONDITION. 

mercurous  nitrate,  may  be  employed  in  making 


the  tests. 

1.  HC1,  hydrochloric  acid,  or  a  soluble  chloride  precipi- 
tates  from  solutions  of  mercurous  salts  white,  pulverulent 
Hg2Cl2,  mercurous  chloride  (calomel),  insoluble  in  water  and 
in  cold  dilute  acids,  easily  soluble  in  nitro-hydrochloric  acid 
(aqua  regia),  with  the  formation  of  HgCl2,  mercuric  chloride 
(corrosive  sublimate)  : 

3Hg2Cl2  +  2HNOS  +  6HC1  =  6HgCl2  +  2NO  +  4H2O. 
Ammonium  hydroxide  converts  the  Hg2Cl2,  mercurous  chlo- 
ride, into   black   NH2Hg2Cl,  dimercurous  ammonium  chlo- 
ride, insoluble  in  excess  of  the  reagent  : 

Hg2Cl2  +  2NH4OH  =  NH2Hg2Cl  +  NH4C1  +  2H2O. 

2.  NaOH,  sodium   hydroxide,  or   KOH,  potassium   hy- 
droxide, precipitates  black  Hg2O,  mercurous  oxide,  insoluble 
in  excess  of  the  reagent. 

3.  NH4OH,  ammonium  hydroxide,  produces  in  solutions 
of  mercurous  salts  a  black  precipitate  containing  nitrogen, 
depending  in  composition  upon  the  mercurous  salt  employed 
and  the  conditions  under  which  precipitation  has  occurred. 
For  example,  on  adding  ammonium  hydroxide  to  a  solution 
of  Hg2(NO3)2,  mercurous  nitrate,  black  NH2Hg2NO3,  dimer- 


12 

curous  ammonium  nitrate  (mercurius  solubilis  Hahnemanni), 
is  formed : 

Hg2(N03)2  +  2NH4OH  =  NH2Hg2N03  +  NH4NO3  +  2H2O. 
The  precipitate  is  insoluble  in  excess  of  the  reagent. 

4.  H2S,  hydrogen  sulphide,  as  well  as  (NH4)2S,  ammonium 
sulphide,  produces  a  black  precipitate,  consisting  of  a  mix- 
ture of  HgS,  mercuric  sulphide,  and  metallic  mercury  (not 
Hg2S,  mercurous  sulphide).     On  boiling  this  precipitate  with 
concentrated    nitric   acid,  a  white   compound    composed  of 
HgS,    mercuric    sulphide,  and   Hg(NO3)2,  mercuric    nitrate 
[Hg3S2(NO3)2],(1)  insoluble  in  nitric  acid,  is  formed,  while  the 
liquid  (nitrate)  contains  Hg(NO3)2,  mercuric  nitrate.     Yellow 
ammonium  sulphide,  (NHJ^,  converts  the  mixture  of  HgS 
and  metallic  mercury  wholly  into  HgS,  mercuric  sulphide. 
Yellow  sodium  sulphide,  Na-jS^,  as  well  as  yellow  potassium 
sulphide,  K2SX,  converts  the  mixture  into  HgS,  mercuric  sul- 
phide.    The  precipitate  is  soluble  in  nitro-hydrochloric  acid. 

5.  SnCl2,  stannous  chloride,(2)  added  in  very  small  quantity 
to  a  concentrated  solution  of  a  mercurous  salt,  precipitates, 
precisely  as  any  other  soluble  chloride,  white  Hg2Cl2,  mercu- 
rous chloride ;  when  added  in  excess,  a  grayish  precipitate  of 
finely-divided  metallic  mercury  is  formed : 

SnCl2  +  2HC1  +  Hg2(NO3)2  =  Hg2  +  SnCl4  +  2HNO3. 

6.  KI,  potassium   iodide,   added  in  small  quantity  to  a 
solution  of  a  mercurous  salt,  precipitates  greenish,  flocculent 
Hg2I2,  mercurous  iodide,  which  in  excess  of  the  reagent  dis- 
solves, with  the  separation  of  metallic  mercury  and  the  for- 
mation of   soluble  HgI2(KI)2,  potassium   mercuric   iodide; 
therefore,  when  much  potassium  iodide  is  added  to  a  dilute 

<S-HgNOs 
^S— HgNO3. 

2SnCl2,  stannous  chloride,  used  as  a  reagent,  always  contains  some  free 
HC1,  hydrochloric  acid. 


13 

solution  of  a  mercurous  salt,  there  immediately  appears  a 
grayish  precipitate  of  metallic  mercury. 

7.  A  drop  or  two  of  a  solution  of  a  mercurous  salt  placed 
on  clean  copper  foil  produces  a  discoloration,  due  to  the  de- 
position of  metallic  mercury,  which  upon  being  gently  rubbed 
with  the  finger  becomes  silvery  white  and  mirror-like  in  ap- 
pearance.    On  heating  the  foil  over  the  flame  the   deposit 
disappears. 

8.  Mercurous  salts  (with  the  exception  of  Hg2Cl2,  mercu- 
rous chloride,  which  volatilizes  unchanged),  when  heated  in  a 
small  dry  glass  reduction-tube  with  dry  Na2CO3,  sodium  car- 
bonate, yield  a  sublimate  consisting  of  globules  of  metallic 
mercury. 

LEAD,   Pb   (PLUMBUM). 
Atomic  weight,  2O6.39;  valence,  II. 

Bluish-white  metal ;  specific  gravity,  11.3;  melting-point, 
334°  C. 

Pb(C2HB02)2,  plumbic  acetate,  may  be  employed  in  making 
the  tests. 

1.  HC1,  hydrochloric  acid,  or  a  soluble  chloride  precipi- 
tates, in  solutions  not  too  dilute,  white,  flocculent  (sometimes 
crystalline)  PbCl2,  plumbic  chloride ;  soluble  at  12.5°  C.  in 
135  parts  of  water,  and  at  the  boiling-point  in  30  parts  of 
water.     On  cooling  the  hot  saturated  aqueous  solution,  the 
lead  salt  crystallizes  in  glistening  rhombic  needles.     It  is 
insoluble  in  ammonium  hydroxide ;    soluble  with  difficulty 
in  dilute  acids;  easily  soluble  in  strong  hydrochloric  acid, 
particularly  on  heating. 

2.  NaOH,  sodium  hydroxide,  as  well  as  KOH,  potassium 
hydroxide,  precipitates  white,  flocculent  Pb(OH)2,  plumbic 
hydroxide  (mixed  with  a  slight  quantity  of  basic  lead  salt), 

2 


14 

— insoluble  in  ammonium  hydroxide ;  slightly  soluble  in 
water;  and  easily  soluble  in  excess  of  sodium  or  potassium 
hydroxide,  with  the  formation  of  Pb(ONa)2,  sodium  plum- 
bite,  (1)  or  Pb(OK)2,  potassium  plumbite  : 

Pb(OH)2  -f  2NaOH  -  Pb(ONa)2  +  2H2O. 

3.  NH4OH,  ammonium  hydroxide,  precipitates  white,  floc- 
culent  Pb(OH)2,  plumbic  hydroxide,  insoluble  in  excess  of 
the  reagent. 

4.  H2S,  hydrogen  sulphide,  or  (NH4)2S,  ammonium  sul- 
phide, precipitates  black  PbS,  plumbic  sulphide,  insoluble  in 
dilute  acids.     Boiling  nitric  acid  converts  it  into  Pb(NO3)2, 
plumbic  nitrate ;    boiling  fuming  nitric  acid  oxidizes  it  to 
PbSO4,  plumbic  sulphate,  which  is  almost  insoluble  in  nitric 
acid.     On   rapidly  passing  H2S,  hydrogen  sulphide,  into  a 
dilute   solution   of  lead   containing   free  hydrochloric  acid, 
cinnabar-red  Pb2SCl2,  plumbic  sulphochloride,(2)  is  often  pro- 
duced.    By  the  further  addition  of  H2S,  the  plumbic  sulpho- 
chloride  is  converted  into  black  PbS : 

2PbCl2  +  H2S  =  Pb2SCl2  -f  2HC1 ; 
Pb2SCl2  +  H2S  =  2PbS  +  2HC1. 

5.  K2CrO4,  potassium  chromate,  as  well  as  K2Cr2O7,  potas- 
sium bichromate,  precipitates  yellow  PbCrO4,  plumbic  chro- 
mate (chrome-yellow),  insoluble  in  water  and  in  HC2H3O2, 
acetic  acid,  difficultly  soluble  in  nitric  acid,  easily  soluble  in 
sodium  or  potassium  hydroxide  : 

PbCr04  +  4NaOH  =  Na2CrO4  +  Pb(ONa)2  +  2H2O. 

6.  H2SO4,  sulphuric  acid,  precipitates  white,  pulverulent 
PbSO4,  plumbic  sulphate,  soluble  in  22,800  parts  of  pure 
water  at  ordinary  temperature,  less  soluble  in  water  containing 
sulphuric  acid,  more  soluble  in  the  presence  of  hydrochloric 


ph  .0-Na  2  o^ 

Pb<0_Na.  S<Pb_Cl. 


15 

or  nitric  acid.  The  precipitate  is  soluble  in  warm  concentrated 
sulphuric  acid,  and  separates  on  diluting  the  solution  with 
water.  It  is  easily  soluble  in  NH4C2H3O2,  ammonium 
acetate,  and  in  the  presence  of  ammonium  hydroxide  in 
(NH4)2C4H4O6,  neutral  ammonium  tartrate,  and  from  these 
solutions  the  lead  may  be  precipitated  by  K2CrO4,  potassium 
chromate,  as  yellow  PbCrO4,  plumbic  chromate. 

7.  KI,  potassium    iodide,  produces  in    solutions   not  too 
dilute  a   yellow,  pulverulent   precipitate   of   PbI2,  plumbic 
iodide,  soluble  in  1235  parts  of  cold  water  and  in  194  parts 
of  boiling  water.     The  plumbic  iodide  separates  from  a  hot 
saturated  solution,  to  which  a  small  quantity  of  HC2H3O2, 
acetic  acid,  has  been  added,  in  glistening,  golden-yellow,  six- 
sided  plates. 

8.  Na2HPO4,   sodium   hydrogen   phosphate,   precipitates 
white,  flocculent  Pb3(PO4)2,  plumbic   phosphate,  soluble  in 
nitric  acid  and  in  sodium  hydroxide,  insoluble  in  acetic  acid. 

9.  Compounds  of  lead  fused  with  sodium  carbonate  in  the 
reducing  flame  on  charcoal  yield  a  white,  ductile  globule  of 
metallic  lead  together  with  a  yellow  incrustation  of  PbO, 
plumbic  oxide. 


SECOND    GROUP. 

Metals  precipitated  from  acid  solutions  as  sulphides  by 
H2S,  hydrogen  sulphide :  Mercuric  Salts,  Copper,  Bismuth, 
Arsenic,  Antimony,  Tin,  Cadmium,  Gold,  and  Platinum. 

MERCURY,   Hg  (HYDRARGYRUM). 
Atomic  weight,  199.8;  valence,  II. 

BEHAVIOR   OF   MERCURY   IN   THE   MERCURIC   CONDITION. 

HgCl-2,  mercuric  chloride,  or  Hg(NO^)2,  mercuric  nitrate, 
may  be  employed  in  making  the  tests. 


16 

1.  H2S,  hydrogen  sulphide,  and  also  (NH4)2S,  ammonium 
sulphide,  produce  in  solutions  of  mercuric  salts  a  white  pre- 
cipitate of  Hg3S2Cl2(l)  or  Hg3S2(NO3y2>  which,  on  the  further 
addition  of  the  reagent,  becomes  yellow,  then  brown,  and 
finally  is  converted  into  black  HgS,  mercuric  sulphide : 

3HgCl2  +  2H2S  =  Hg3S2Cl2  +  4HC1 ; 
Hg3S2Cl2  +  H2S  =  3HgS  -f  2HC1. 

HgS  is  not  dissolved  by  ammonium  sulphide ;  sometimes, 
however,  on  being  treated  with  ammonium  sulphide,  it  is 
converted  from  black  HgS  into  red  HgS  (cinnabar). 

Na^S,  sodium  sulphide,  and  K2S,  potassium  sulphide  (par- 
ticularly in  the  presence  of  sodium  or  potassium  hydroxide), 
dissolve  mercuric  sulphide,  with  the  formation  of  HgS2Na2(3) 
or  HgS2K2.«> 

Mercuric  sulphide  is  insoluble  in  boiling  hydrochloric  acid 
or  in  nitric  acid,  but  by  the  continued  action  of  hot  concen- 
trated nitric  acid  it  is  converted  into  the  white  insoluble 
double  salt  Hg3S2(NO3)2  (as  in  the  case  of  Hg2S,  mercurous 
sulphide). 

Nitro-hydrochloric  acid  dissolves  mercuric  sulphide,  with 
the  formation  of  HgCl2,  mercuric  chloride : 
3HgS  4-  6HC1  +  2HN03  =  3HgCl2  +  2NO  +  4H2O  +  S3. 

2.  NaOH,  sodium  hydroxide,  and  KOH,  potassium  hy- 
droxide, produce  a  brownish-red  precipitate  of  a  basic  salt, 
which,  upon  further  addition  of  the  reagent,  is  converted  into 
yellow  HgO,  mercuric  oxide. 

3.  NH4OH,  ammonium  hydroxide,  produces  a  white  pre- 
cipitate ;   thus,  in   a  solution  of  HgCl2,  mercuric  chloride, 
white  NH2HgCl,  mercuric  ammonium  chloride  is  produced : 


17 

HgCl2  +  2NH4OH  =  NH2HgCl  +  NH4C1  +  2H2O. 

4.  SnCl2,  stannous  chloride,  added  in  small  quantities  to 
mercuric  chloride  or  to  mercuric  salts  containing  a  very  slight 
quantity  of  free  hydrochloric  acid,  precipitates  white  Hg2Cl2, 
mercurous  chloride,  which,  on  the  addition  of  more  stannous 
chloride,  is  reduced  to  gray,  finely-divided,  metallic  mercury 
(very  delicate  reaction). 

5.  KI,  potassium  iodide,  precipitates  red  HgI2,  mercuric 
iodide,  soluble  in  excess  of  the  reagent,  with  the  formation 
of  HgI2(KI)2,  potassium  mercuric  iodide. 

6.  A  drop  or  two  of  a  solution  of  a  mercuric  salt  placed 
on  clean  copper  foil  produces  a  discoloration,  due  to  the  depo- 
sition of  metallic  mercury,  as  in  the  case  of  mercurous  salts. 
On  gently  rubbing  the  spot  it  becomes  mirror-like  in  appear- 
ance, and  on  heating  the  foil  the  spot  disappears,  due  to  the 
volatilization  of  the  mercury. 

7.  Many  of  the  mercuric  salts,  when  heated  in  a  glass  re- 
duction-tube, sublime  undecomposed,  as,  for  example,  HgCl2, 
mercuric  chloride  (corrosive  sublimate),  while  others  yield 
sublimates  whic.li,  because  of  an  admixture  of  basic  salts,  are 
colored  yellow.     If  the  white  (or  yellow)  sublimate  be  covered 
with  dry  sodium  carbonate  and  again  heated,  red  mercuric 
oxide  is  produced,  which,  on  being  more   strongly  heated, 
breaks  up  into  metallic  mercury  and  oxygen. 

COPPER,  Cu  (CUPRUM). 
Atomic  weight,  63.18;  valence,  II. 

Reddish  metal ;  specific  gravity,  8.94 ;  melting-point,  1054° 
C. 

CuSOt,  cupric  sulphate,  may  be  employed  in  making  the  tests. 

1 .  H2S,  hydrogen  sulphide,  or  (NH4)2S,  ammonium  sulphide, 
precipitates  black  CuS,  cupric  sulphide,  insoluble  in  dilute 

"  b  2* 


18 

acids,  insoluble  in  N^S,  sodium  sulphide,  and  in  K2S,  potas- 
sium sulphide.  Ammonium  sulphide  (particularly  the  yellow 
ammonium  sulphide)  dissolves  traces  of  the  precipitate,  with 
the  formation  of  Cu^NHJ,  =  (CuS)2(NH4)2S5.  Boiling 
nitric  acid  dissolves  CuS,  with  the  formation  of  Cu(NO3)2, 
cupric  nitrate.  It  is  also  soluble  in  KCN,  potassium  cyanide  : 

2CuS  +  4KCN  =  Cu2C4N4K2  +  K2S2. 
The  precipitate  (CuS),  when  moist  and  exposed  to  the  air, 
readily  absorbs  oxygen,  with  the  formation  of  CuSO4,  cupric 
sulphate. 

2.  NaOH,   sodium   hydroxide,  or   KOH,  potassium  hy- 
droxide, produces  in  cold  solution  a  voluminous  flocculent 
precipitate  of  bluish-white  Cu(OH)2,  cupric  hydroxide,  insol- 
uble in  excess  of  the  reagent,  but  easily  soluble  in  ammonium 
hydroxide.     The  precipitate,  on  being  boiled  with  excess  of 
sodium  or  potassium  hydroxide,  loses  water  and  forms  black 
CuO,  cupric  oxide.     On  adding  sodium  or  potassium  hydrox- 
ide to  copper  solutions  containing  non-volatile  organic  acids, 
and  particularly  containing  such  organic  substances  as  glucose, 
(grape  sugar,)  glycerin,   etc.,  and  agitating  the  liquid,  the 
bluish-white  cupric  hydroxide  at  first  produced  is  immediately 
dissolved,  with  the  production  of  a  deep-blue  liquid. (l) 

3.  NH4OH,  ammonium  hydroxide,  added  in  small  quanti- 
ties, produces  a  bluish- white  precipitate  of  a  basic  salt,  which 
is  soluble  in  an  excess  of  the  reagent,  producing  a  deep-blue 


1  This  property  is  made  use  of  in  the  preparation  of  an  alkaline  copper 
solution  in  which  cupric  sulphate  solution  is  added  to  a  strong  sodium 
hydroxide  solution  containing  KNaC4H4O6,  potassium  sodium  tartrate 
(Rochelle  salt),  the  whole  forming  a  deep-blue  liquid  (Fehling's  solution), 
which  is  employed  as  a  reagent  for  the  detection  of  glucose  (grape  sugar). 
On  boiling  a  solution  containing  glucose  to  which  Fehling's  solution  has 
been  added,  insoluble  red  Cu2O,  cuprous  oxide,  or  yellow  Cu2(OH)2,  cuprous 
hydroxide,  separates. 


19 

solution,  due  to  the  formation  of  Cu(NH3)4SO4,  cupric  am- 
monium sulphate  (very  delicate  reaction).  Strong  acid  solu- 
tions are  not  generally  precipitated  by  ammonium  hydroxide. 

4.  Na2HPO4,    sodium    hydrogen    phosphate,    produces   a 
bluish-green,  flocculent  precipitate  of   Cu3(PO4)2,  soluble  in 
ammonium  hydroxide. 

5.  K4Fe(CN)6,  potassium  ferrocyanide,  precipitates  brown- 
ish-red Cu2Fe(CN)6,  cupric  ferrocyanide  (very  delicate  reac- 
tion). 

6.  KCN,  potassium  cyanide,  added  in  excess  to  a  neutral 
or  ammoniacal  solution  of  a  salt  of  copper,  produces  a  color- 
less solution  of  Cu2(CN)2(KCN)2,  potassium  cuprous  cyanide  : 

Cu(NO3)2  +  2KCN  =  Cu(CN)2  -f  2KNO3 ; 

Cu— C2N2— K 

2Cu(CN)2-f2KCN=    I  +  C2N2. 

Cu— C2N2— K 

The  copper  of  this  potassium  salt  of  hydrocuprocyanic 
acid(1)  is  not  precipitated  by  hydrogen  sulphide  (correspond- 
ing to  the  iron  in  potassium  ferro-  and  ferricyanide,  which  is 
not  precipitated  by  the  ordinary  reagents). 

7.  A  bright  piece  of  iron  (knife-blade)  free  from  grease 
placed  in  a  solution  of  copper  is  soon  covered  with  a  reddish 
deposit  of  metallic  copper. 

8.  Compounds  of    copper   mixed  with  sodium  carbonate 
and  strongly  heated  on  charcoal  in  the  reducing  flame  yield 
reddish  spangles  or  globules  of  metallic  copper. 

9.  Compounds  of  copper  fused  in  a  bead  of  borax,  Na2B4O7, 
held  in  a  loop  of  platinum  wire  in  the  oxidizing  flame  of  the 
blowpipe,  yield  a  bluish-green  bead.      Fused  in  a  bead  of 
sodium  ammonium   phosphate,  NaNH4HPO4  (microcosmic 


Cu— C,N2— H. 


20 

salt),  they  yield,  in  the  oxidizing  flame,  a  bluish-green  bead, 
which,  when  heated  in  the  reducing  flame,  becomes  reddish 
brown  and  opaque,  due  to  the  presence  of  separated  metallic 
copper.  The  addition  to  the  bead  of  a  little  metallic  tin 
facilitates  the  reduction. 

BISMUTH,  Bi. 
Atomic  weight,  2O7.5;   valence,  III. 

Reddish-white  metal  ;  specific  gravity,  9.82  ;  melting-point, 
270°  C. 


or  BiCl3  may  be  employed  in  making  the  tests. 

1.  H,jS,  hydrogen  sulphide,  or  (NH4)2S,  ammonium  sul- 
phide, precipitates  brownish-black  BijS3,  bismuth  sulphide, 
insoluble  in  dilute  acids  and  in  ammonium  sulphide.     It  is 
dissolved  by  boiling  nitric  acid,  forming  Bi(NO3)3,  bismuth 
nitrate. 

2.  NaOH,  sodium  hydroxide,  KOH,  potassium  hydroxide, 
or  NH4OH,  ammonium  hydroxide,  precipitates  white,  amor- 
phous BiO-OH,  bismuth  hydroxide,  insoluble  in  excess  of 
the  reagent. 

3.  K2CrO4,  potassium  chromate,  precipitates  yellow,  crys- 
talline  Bi2O(CrO4)2,  basic    bismuth   chromate,    insoluble   in 
sodium  hydroxide,  soluble  in  nitric  acid. 

4.  A  clear  solution  of  a  bismuth  salt,  when  poured  into  a 
large  quantity  of  water  (provided  the  bismuth  solution  does  not 
contain  too  much  free   acid),  produces  a  milky  turbidity,  due 
to  the  separation  of  a  white  basic  salt  of  bismuth.     BiCl3,  bis- 
muth chloride,  yields  BiOCl,  bismuth  oxychloride.     Bi(NO3)3, 
bismuth  nitrate,  yields  first  BiONO3,  bismuth  oxynitrate,  and 
afterwards,  especially  on  heating  the  liquid,  Bi2O2NO3OH.  (1) 


OH 


21 

A  few  drops  of  hydrochloric  acid  or  of  NH4C1,  ammonium 
chloride,  added  to  a  bismuth  nitrate  solution  before  it  is 
poured  into  the  water,  causes  the  separation  of  the  bismuth 
as  BiOCl,  bismuth  oxychloride.  The  reaction  with  BiCl3  is 
the  more  delicate.  Tartaric  acid  does  not  interfere  with  this 
reaction. 

5.  Bismuth  salts,  mixed  with  sodium  carbonate  and  heated 
in  the  reducing  flame  on  charcoal,  yield  brittle  globules  of  me- 
tallic bismuth  and  a  yellow  incrustation  of  Bi2O3,  bismuthous 
oxide. 

ARSENIC,  As  (ARSENICUM). 
Atomic  weight,  74.9;  valence,  III,  V. 

Steel-gray  non-metal ;  specific  gravity,  5.72  at  14°  C. 

Arsenic  forms  two  compounds  with  oxygen, — As2O3,  arsen- 
ious  oxide  or  anhydride,  and  As2O5,  arsenic  oxide  or  anhy- 
dride. 

BEHAVIOR   OF   ARSENIC   IN    THE   ARSENIOUS    CONDITION, — 
AS   ARSENIOUS   ACID. 

As203,  arsenious  oxide,  which,  when  dissolved  in  water,  forms 
H3As03,  arsenious  acid,  may  be  employed  in  making  the  tests. 

1.  H2S,  hydrogen  sulphide,  precipitates,  from  w^arm  solu- 
tions acidulated  with  hydrochloric  acid,  yellow  As2S3,  arseni- 
ous sulphide,  which  is  soluble  in  ammonium  sulphide  and  in 
(NH4)2CO3,  ammonium  carbonate,  but  is  insoluble  in  hydro- 
chloric acid.  Dissolved  in  ordinary  colorless  ammonium 
sulphide  it  forms  (NH4)3AsS3,  ammonium  sulpharsenite,  and 
from  this  solution  it  may  be  reprecipitated  by  acids  as  As2S3, 
arsenious  sulphide : 

2(NH4)3AsS3  +  6HC1  =  As2S3  +  6NH4C1  +  3H2S. 
Dissolved  in  yellow  ammonium  sulphide  it  forms  (NH4)3AsS4, 
ammonium  sulpharseniate.     From  this  solution  it  is  precip- 
itated by  acids  as  As2S5,  arsenic  sulphide : 


4 


22 

3(NH4)2S  +  S2  =  2(NH4)3AsS 
2(NH4)3AsS4  +  6HC1  =  AS&  +  6NH4C1  +  3H2S. 
Ammonium  carbonate  dissolves  As2S3  with  the  formation 
of  ammonium  sulpharsenite  and  ammonium  arsenite  : 
As&  +  3(NH4)2C03  =  (NH4)3AsS3  +  (NH4)3ASO3  +  3CO2. 
Acids  reprecipitate  it  from  this  solution  as  As2S3  : 
(NH4)3AsS3  +  (NH4)3As03  +  6HC1  =  As2S3  -f  6NH4C1  + 

3H20. 

As2S5,  arsenic  sulphide,  dissolved  in  ammonium  carbonate 
forms  ammonium  sulpharseniate  and  ammonium  arseniate  : 
4AS&  -f  12(NH4)2C03  =  5(NH4)3AsS4  +  3(NH4)3AsO4  + 

12CO2. 

From  this  solution  acids  reprecipitate  it  as  As2S5  : 
5(NH4)3AsS4  +  3(NH4)3AsO4  +  24HC1  =  4As2S5  -f-  24NH4C1 

4-  12H20. 

2.  AgNO3,  argentic  nitrate,  added  to  an  aqueous  solution 
of  arsenious  acid  and  ammonium  hydroxide  added  drop  by 
drop  produces  a  yellow,  curdy  precipitate  of  Ag3AsO3,  ar- 
gentic  arsenite,  soluble   in   nitric   acid   and   in    ammonium 
hydroxide. 

3.  CuSO4,  cupric  sulphate,  added  to  an  aqueous  solution 
of  arsenious  acid,  and  ammonium  hydroxide  subsequently 
added  drop  by  drop,  produces  a  greenish,  flocculent  precipi- 
tate of  CuHAsO3,  cupric  arsenite  (Scheele's  green),  soluble  in 
excess  of  ammonium  hydroxide  and  in  acids. 

4.  Marsh's  Test.  —  When  a  few  drops  of  a  solution  of  ar- 
senious acid  or  a  soluble  arsenite  are  placed  in  an  apparatus 
in  which  hydrogen  is  being  evolved,  the  nascent  hydrogen 
reduces  the  arsenical  compound,  and  gaseous  AsH3,  hydrogen 
arsenide  (arsenu  retted  hydrogen),  is  evolved  with  the  free 
hydrogen  : 

H3AsO3  +  3Zn  +  3H2SO4  =  AsH3  -f  3ZnSO4  -f  3H2O. 
When  this  mixture  of  hydrogen  and  hydrogen  arsenide  is 


23 

slowly  passed  through  a  glass  tube  heated  to  incipient  red- 
ness, the  hydrogen  arsenide  is  decomposed,  and  the  arsenic  is 
deposited  in  the  metallic  state  on  the  inner  surface  of  the 
tube  just  beyond  the  heated  part,  as  a  lustrous  brown,  gray, 
or  black  coating.  For  this  purpose  the  apparatus  of  Marsh, 
Fig.  1,  is  best  adapted. 

FIG.  1. 


The  apparatus  consists  of  a  small  generating  flask,  A,  a 
drying-tube,  B,(l)  containing  small  pieces  of  calcium  chlo- 
ride, and  a  reduction-tube,  (7,  of  hard  glass,  contracted  at 
intervals. 

The  metallic  zinc  and  concentrated  sulphuric  acid  (diluted 
with  about  four  volumes  of  water)  used  in  the  operation 
must  be  free  from  arsenic,  and  therefore  the  following  con- 
trol test  should  always  be  made  to  determine  their  purity. 
Zinc  is  placed  in  the  flask  A,  and  the  drying-tube  .5,  to- 
gether with  the  reduction-tube  (7,  is  connected  with  the 
flask.  Dilute  sulphuric  acid  (1-4)  is  introduced  through  the 
funnel-tube  until  the  zinc  is  covered.  When,  after  some 
minutes,(2)  the  evolved  hydrogen  has  expelled  the  air  from  the 

1  The  drying-tube  is  sometimes  dispensed  with,  and  the  reduction-tube 
connected  directly  with  the  delivery-tube  of  the  flask. 

2  If  the  action  is  slow,  as  is  usually  the  case  when  pure  zinc  is  em- 
ployed, it  may  be  accelerated  by  the  addition  of  a  few  drops  of  platinic 
chloride. 


24 

entire  apparatus/1*  the  flame  of  a  Bunsen  burner  is  applied  to 
that  part  (at  D)  of  the  reduction-tube  between  the  contracted 
portion  and  the  drying-tube,  and  the  tube  then  heated  to 
incipient  redness.  After  the  flame  has  been  applied  for  sev- 
eral minutes,  the  contracted  part  of  the  reduction-tube  is  ex- 
amined for  the  presence  of  a  brownish,  gray,  or  black  lus- 
trous deposit.  Should  such  a  deposit  be  found,  it  indicates 
that  either  the  zinc  or  the  sulphuric  acid,  or  both,  are  con- 
taminated with  arsenic  and  therefore  unfit  for  use  in  the  test. 

If  no  deposit  is  produced  by  the  above  test,  the  application 
of  the  heat  is  continued,  and  the  solution  containing  arsenic 
is  introduced  into  the  flask,  through  the  funnel-tube.  After 
the  lapse  of  some  minutes  the  contracted  part  of  the  tube 
immediately  beyond  the  flame  is  examined  for  the  presence 
of  a  brownish,  gray,  or  black  deposit. (2)  A  deposit  having 
formed,  the  reduction-tube  is  detached  (leaving  it  open  at 
both  ends,  to  permit  the  free  access  of  air),  inclined  over  a 
small  flame,  and  gently  heated  at  the  part  containing  the 
deposit.  The  arsenic  volatilizes,  combines  with  oxygen,  and 
deposits  beyond  the  part  heated,  as  As2O3,  arsenious  oxide,  in 
minute  octahedral  crystals/3^ 

If  the  gas  is  ignited  as  it  escapes  from  the  contracted  end 
of  the  tube,  and  the  temperature  of  the  flame  is  reduced  by 
holding  a  piece  of  cold  porcelain  in  it,  incomplete  combustion 

1  Unless  the  air  is  expelled,  an  explosion,  which  may  cause  personal 
injury,  is  likely  to  occur  when  the  flame  is  applied  to  the  reduction- 
tube. 

2  Antimony  yields  a  deposit  much  resembling  in  color  that  produced 
by  arsenic.     The  arsenical  deposit  is  soluble  in  fresh   NaOCl,  sodium 
hypochlorite,  whereas  the  antimony  deposit  is  insoluble  in  that  reagent. 

3  The  antimony  deposit  volatilizes  and  yields  a  white  sublimate,  which 
is  generalty  amorphous,  or  consists  of  minute  granules  and  opaque  gran- 
ular masses ;  but  it  may  contain  well-defined  octahedral  crystals  of  Sb2O3, 
antimonious  oxide. 


25 

occurs,  and  the  arsenic  is  deposited  on  the  porcelain  in  the 
metallic  state  in  lustrous  brown,  gray,  or  black  spots : 

2AsH3  +  O3  =  As2  +  3H2O. 

The  arsenical  deposit  is  soluble  in  fresh  NaCIO,  sodium  hy- 
pochlorite.  (Distinction  from  antimony.) 

As2  H-  SNaOCl  +  3H2O  =  2H3AsO3  +  3NaCl. 

As  hydrogen  arsenide  is  exceedingly  poisonous,  it  should 
not  be  allowed  to  escape  in  the  room,  but  should  be  decom- 
posed by  igniting  it  as  it  escapes  from  the  tube,  or  conducting 
it  into  a  solution  of  argentic  nitrate,  whereby  reduction  of  the 
silver  salt  occurs  with  the  separation  of  metallic  silver,  the 
arsenic  remaining  in  solution  : 

AsH3  +  6  AgNOs  +  3H2O  —  6  Ag  +  H3AsO3  +  6HNO8. 

5.  Reinsch's  Test. — Metallic  copper  reduces  arsenious  oxide 
in  acid  solution  to  metallic  arsenic,  which  is  deposited  on  the 
copper  as  Cu5As2,  cupric  arsenide.  The  arsenical  solution  is 
acidulated  with  about  one-seventh  of  its  volume  of  hydro- 
chloric acid,  a  clean  piece  of  copper  foil  placed  in  the  solution, 
and  the  whole  heated  and  kept  almost  at  the  boiling-point 
for  several  minutes.  In  this  hot  solution  the  arsenic  is 
deposited  on  the  foil  as  a  grayish  or  black  coating.  The  foil 
is  taken  from  the  liquid  and  im- 
mersed several  times  in  water  to 
wash  off  the  hydrochloric  acid, 
then  pressed  (without  rubbing) 
between  filter  paper  to  free  it  from 
adherent  moisture,  and  finally 
completely  dried  by  being  heated 
in  a  porcelain  dish  on  a  water-  • 
bath.  It  is  then  placed  in  a 

reduction-tube  near  the  contracted  part,  the  tube  inclined, 
and  the  part  containing  the  foil  gently  heated  over  a  small 
flame  (Fig.  2). 


26 

Volatilization  of  the  arsenic  and  combination  with  oxygen 
take  place,  and  octahedral  crystals  of  As2O3,  arsenious  oxide, 
are  deposited  in  the  cooler  part  of  the  tube. 

6.  Arsenious  oxide  heated   in  a  reduction-tube  sublimes 
unchanged,  and  is  deposited  in  the  cooler  portion  of  the  tube 
in  octahedral  crystals.     Heated  in  a  dry  reduction-tube  with 
charcoal,  a  grayish  or  black  mirror-like  deposit  of  metallic 
arsenic  is  formed  in  the  cooler  part  of  the  tube : 

As2O3  +  C3  =  As2  + SCO. 

7.  Arsenious  oxide  or  compounds  of  arsenic  heated  on 
charcoal  in  the  reducing  flame  produce  a  garlic-like  odor. 
(The  arsenious  oxide  is  first  reduced  to  metallic  arsenic,  which 
volatilizes  and  combines  with  oxygen  to  form  As2O3,  which 
sometimes  collects  as  an  incrustation  on  the  charcoal.) 

8.  Arsenious  oxide  or  an  arsenite,  mixed  with  six  times  its 
bulk  of  a  dry  mixture  consisting  of  equal  parts  of  sodium 
carbonate  and  potassium  cyanide  and  heated  in  a  reduction- 
tube,  is  reduced,  with  the  formation  of  a  black  glistening 
sublimate  of  metallic  arsenic  in  the  cool  part  of  the  tube. 


ARSENIC   ACID. 

As205,  arsenic  oxide,  which,  dissolved  in  water,  forms 
H3As04,  arsenic  acid;  or  Na3As04,  sodium  arseniate,  may  be 
employed  in  making  the  tests. 

1.  H2S,  hydrogen  sulphide,  does  not  at  first  produce  a 
precipitate,  but  reduces  the  arsenic  acid  to  arsenious  acid. 
Heating  the  solution  facilitates  the  reduction : 

As.2O5  -f  2H2S  =  As2O3  +  2H2O  +  S2. 

Continuing  the  addition  of  hydrogen  sulphide,  As2S3,  arsen- 
ious sulphide,  is  precipitated : 

3H2S  =  As2S3  +  3H2O. 


27 

The  final  precipitate  is  therefore  a  mixture  of  arsenious  sul- 
phide and  sulphur  (As2S3  -j-  S2). 

2.  AgNO3,  argentic  nitrate,  added  to  a  solution  of  arsenic 
acid  which   has   been   exactly  neutralized   with   ammonium 
hydroxide,    or   to   an   arseniate,    precipitates   reddish-brown 
Ag3AsO4,  argentic  arseniate,  soluble  in  nitric  acid  and  in 
ammonium  hydroxide : 

H3AsO4  +  3AgNO3  -f  3NH4OH  t*  Ag3AsO4  +  3HN4NO3 
+  3H20. 

3.  CuSO4,  cupric  sulphate,  added  to  a  solution  of  arsenic 
acid,  followed  by  the  addition  of  ammonium  hydroxide  drop 
by  drop,  or  to  an  arseniate,  produces  a  bluish-green  precipi- 
tate of  CuHAsO4,  cupric  arseniate,  soluble  in  an  excess  of 
ammonium  hydroxide  and  in  acids. 

4.  The  behavior  of  arsenic  acid  in  Marsh's  test  or  Reinsch's 
test,  in  the  reduction-tube,  mixed  with  charcoal,  and  on  char- 
coal itself  is  identical  with  arsenious  acid. 

5.  MgSO4,  magnesium  sulphate,  added  to  a  solution  of  ar- 
senic acid  or  an  arseniate,  followed  by  the  addition  of  NH4C1, 
ammonium  chloride,(1)  and  ammonium  hydroxide  (magnesia 
mixture),  precipitates  white,  crystalline  MgNH4AsO4  -f-  6H2O, 
ammonium  magnesium  arseniate : 

H3As04  +  MgS04  -f  3NH4OH  =  MgNH4AsO4 -f-  (NH4)2SO4 

-f  3H20. 

In  concentrated  solutions  the  precipitate  forms  immediately, 
and  in  dilute  solutions  gradually ;  but  is  always  perceptibly 
crystalline.  It  is  soluble  in  15,293  parts  of  cold  water  and 
less  soluble  in  water  containing  ammonium  hydroxide ;  easily 
soluble  in  dilute  acids,  from  which  solutions  it  is  reprecipitated 
by  the  addition  of  ammonium  hydroxide. 

1  The  addition  of  ammonium  chloride  is  for  the  purpose  of  preventing 
the  precipitation  of  magnesium  hydroxide. 


28 

6.  NH4HMoO4,  ammonium  molybdate,  added  to  a  solution 
of  arsenic  acid   rather  strongly  acidulated  with  nitric  acid, 
and  the  whole  gently  warmed,  produces  a  yellow  precipitate 
of,  possibly,  (NH4)3AsO4(MoO3)10,  ammonium  molybdoarseni- 
ate,  soluble  in  ammonium  hydroxide  and  reprecipitated  from 
this  solution  by  nitric  acid.     The  presence  of  hydrochloric 
acid  or  of  chlorides  interferes  with  the  delicacy  of  the  reaction. 

7.  To  detect  arsenic  acid  in  the  presence  of  arsenious  acid 
(providing  the  compounds  are  soluble  in  water)  their  behavior 
with  magnesia  mixture  (compare  above,  5)  is  made  use  of; 
arsenious  acid  produces  no  precipitate  with  magnesia  mixture. 
In  case  the  compound  is  insoluble  in  water,  it  is  dissolved  in 
hydrochloric  acid,  and  the  arsenious  acid  is  precipitated  in 
cold  solution  with  hydrogen  sulphide.     The  resulting  arseni- 
ous sulphide  is  removed  by  filtration,  the  filtrate  is  warmed, 
and  hydrogen  sulphide  again  conducted  into  the  liquid.     The 
production  of  a  precipitate  indicates  the  presence  of  arsenic 
acid. 

ANTIMONY,  Sb  (STIBIUM). 
Atomic  weight,  119.6;   valence,  III,  V. 

Silvery-white  metal ;  specific  gravity  6.7  ;  melting-point, 
425°  C. 

Antimony  forms  two  typical  compounds  with  oxygen, — 
Sb2O3,  antimonious  oxide,  and  Sb2O5,  antimonic  oxide. 

BEHAVIOR  OF  ANTIMONY  IN  THE  ANTIMONIOUS   CONDITION. 

SbCl3,  antimonious  chloride,  may  be  employed  in  making  the 


I .  H2S,  hydrogen  sulphide,  produces  in  solutions  of  anti- 
monious salts  which  are  not  too  strongly  acidulated  an  orange- 
red  precipitate  of  Sb2S3,  antimonious  sulphide,  insoluble  in 
dilute  acids,  soluble  in  concentrated  hydrochloric  acid  (without 


29 

the  separation  of  sulphur)  and  also  in  ammonium  sulphide 
and  in  sodium  or  potassium  sulphide ;  insoluble  in  ammonium 
carbonate  (distinction  from  arsenic).  When  dissolved  in 
colorless  ammonium  sulphide  it  forms  (NH4)3SbS3,  ammonium 
sulphantimonite : 

Sb2S3  +  3(NH4)2S  -  2(NH4)3SbS3 ; 

and  when  dissolved  in  yellow  ammonium  sulphide  it  forms 
(NH4)3SbS4,  ammonium  sulphantimonate : 

Sb2S3  +  3(1STH4)2S  +  S2  =  2(NH4)3SbS4. 

Hydrochloric  acid  precipitates  from  the  sulphantimonite  so- 
lution Sb2S3,  and  from  the  sulphantimonate  solution  Sb2S5 : 

2(NH4)3SbS3  +  6HC1  =  Sb2S3  +  6NH4C1  +  3H2S ; 
•  2(NH4)3SbS4  +  6HC1  =  Sb2S5  +  6NH4C1  +  3H2S. 

2.  NaOH,  sodium  hydroxide,  as  well  as  KOH,  potassium 
hydroxide,    produces    a   white    voluminous    precipitate    of 
Sb(OH)3,  antimonious  hydroxide,  readily  soluble  in  an  excess 
of  the  reagent,  forming   SbO(ONa),   sodium  antimonite,   or 
SbO(OK),  potassium  antimonite.     On  being  boiled  in  the 
alkaline  liquid  the  precipitate  of  Sb(OH)3  is  converted  into 
Sb2O3,  antimonious  oxide. 

3.  NH4OH,     ammonium    hydroxide,    precipitates    white 
Sb(OH)3,  antimonious  hydroxide,  insoluble  in  an  excess  of 
the  reagent.     Tartaric  acid  prevents  the  precipitation. 

4.  On   pouring  a  solution  of  an  antimonious  salt,  as,  for 
example,  SbCl3,  antimonious  chloride,  into  a  large  quantity 
of  water,  a  white  precipitate  of  a   mixture  of  SbOCl,   anti- 
monious oxychloride,  and  Sb4O5Cl2  is  produced : 

SbCl3  +  H2O  =  SbOCl  +  2HC1 ; 

4SbCl3  +  5H2O  =  Sb4O5Cl2  -f  10HC1. 

A  milkiness  is  produced  in  water  by  even  the  slightest  quan- 
tity of  antimonious  chloride.  Tartaric  acid  prevents  the  pre- 
cipitation by  dissolving  the  precipitate  : 

SbOCl  +  H2C4H406  =  (SbO)HC4H406  +  HC1. 

3* 


30 

5.  Soluble  salts  of  antimony,  placed  in  a  flask  in  which 
hydrogen  is  being  generated  from  zinc  and  dilute  sulphuric 
acid  (1—4),  are  decomposed,  with  the  formation    of   gaseous 
SbH3,  antimonious  hydride  (antimouuretted  hydrogen) : 

2SbCls  +  Zn6  +  3H2SO4  =  2SbH3  -f  3ZnCl2  +  3ZnSO4. 
The  apparatus  of  Marsh  is  best  adapted  for  this  purpose,  and 
the  same  precautions  as  given  under  arsenic  should  be  ob- 
served.    (See  page  23.) 

On  heating  the  reduction-tube  of  Marsh's  apparatus  to 
dull  redness  and  slowly  passing  antimonious  hydride  through 
the  tube,  the  compound  is  reduced,  and  a  lustrous  brown 
or  black  deposit  of  metallic  antimony  is  formed  in  the  part 
of  the  tube  before  the  flame,  or  on  both  sides  of  the  flame. 
If  the  gas  is  ignited  as  it  escapes  from  the  contracted  end  of 
the  tube  and  the  temperature  of  the  flame  reduced  by  hold- 
ing a  piece  of  cold  porcelain  in  it,  incomplete  combustion 
occurs,  and  the  antimony  is  deposited  on  the  porcelain  in 
dull  brownish  or  black  spots  : 

2SbH3  -f  O3  =  Sb2  -f  3H2O. 

The  deposit  of  metallic  antimony  is  insoluble  in  fresh  sodium 
hypochlorite  (distinction  from  arsenic). 

The  deposit  of  metallic  antimony  in  the  tube,  on  being 
gently  heated  over  a  small  flame  with  free  access  of  air,(1)  vol- 
atilizes, combines  with  oxygen,  and  condenses  in  the  cooler 
part  of  the  tube  as  white  Sb2O3,  antimonious  oxide.  The 
sublimate  is  usually  entirely  amorphous,  but  occasionally 
may  contain  octahedral  crystals  of  antimonious  oxide. 

6.  Compounds  of  antimony  in  acid  solution  are  reduced 
on  being  heated  with  a  piece  of  bright  copper  foil,  with  the 
deposition  of  the  antimony  as  a  grayish  or  black  coating 
upon  the  copper.     On  washing  the  foil  with  water,  drying, 

1  As  in  Marsh's  test  for  arsenic.     (See  page  24.) 


31 

and  gently  heating  it  in  a  small  reduction-tube  over  a  flame, 
the  antimony  volatilizes,  combines  with  oxygen,  and  deposits 
in  the  cooler  part  of  the  tube  as  amorphous  Sb2O3,  antimoni- 
ous  oxide,  which  may  sometimes  contain  octahedral  crystals 
of  antimonious  oxide.  (See  Reinsch's  Test  for  Arsenic, 
page  25.) 

7.  Metallic  zinc  reduces  antimonious  solutions,  the  anti- 
mony separating  as  a  black  powder.     If  a  drop  of  the  anti- 
monious solution  is  placed  on  a  piece  of  platinum  foil  and  a 
small  fragment  of  zinc  is  placed  in  the  solution,  the  antimony 
is  deposited  on  the  foil  as  a  brown  or  black  adherent  coating, 
insoluble  in  hydrochloric  acid  : 

2SbCl3  +  Zns  =  Sb2  -f-  3ZnCl2. 

8.  Compounds  of  antimony,  when  heated  in  the  reducing 
flame   with   sodium   carbonate   on   charcoal,  yield   a  white, 
brittle  globule  of  metallic  antimony,  usually  coated  with  a 
white  incrustation  of  Sb2O3,  antimonious  oxide. 

BEHAVIOR    OF    ANTIMONY    IN    THE    ANTIMONIC    CONDITION. 

SbCl5,  antimonic  chloride,  may  be  employed  in  making  the 

tests. 

1.  H2S,  hydrogen  sulphide,   precipitates  from  acid   solu- 
tions orange-red  Sb2S5,  antimonic  sulphide,  insoluble  in  dilute 
acids  and  in  ammonium  carbonate,  soluble  in  concentrated 
hydrochloric  acid,  forming  SbCl3;  antimonious  chloride  (with 
the  separation  of  sulphur)  : 

Sb2S5  +  6HC1  ==  2SbCl3  +  3H2S  +  S2, 

and  soluble  in  ammonium  sulphide  and  in  sodium  or  potas- 
sium sulphide,  with  the  formation  of  sulphantimonates  : 
Sb2S5  +  3(NH4)2S  =  2(NH4)3SbS4. 

2.  The  behavior  of  antimonic  compounds   is  similar  to 


32 

that  of  antimonious  compounds  in  respect  to  the  tests  with 
zinc  and  dilute  sulphuric  acid,  copper  foil  and  hydrochloric 
acid,  and  platinum  foil  and  zinc. 

3.  To  detect  antimonious  compounds  in  the  presence  of 
antimonic  compounds,  the  behavior  of  an  alkaline  solution 
of  antimonious  oxide  with  a  silver  solution  is  taken  advan- 
tage of.  On  adding  argentic  nitrate  to  the  alkaline  solution 
and  gently  heating  it,  a  precipitate  composed  of  Ag2O, 
argentic  oxide,  and  metallic  silver  is  formed.  Ammonium 
hydroxide  has  the  property  of  dissolving  only  the  argentic 
oxide,  leaving  the  metallic  silver  undissolved  : 

SbO(OK)  +  Ag2O  =  KSbO3  +  Ag2. 

After  washing  the  precipitate  and  then  treating  it  with 
ammonium  hydroxide,  metallic  silver  will  remain  undis- 
solved in  case  an  antimonious  compound  was  originally 
present. 

To  detect  antimonic  compounds  in  the  presence  of  anti- 
monious compounds,  the  alkaline  solution  is  acidulated  with 
hydrochloric  acid,  KI,  potassium  iodide,  added,  and  then 
boiled ;  in  the  presence  of  an  antimonic  compound  iodine  is 
separated  : 

SbCl5  +  2HI  =  SbCl3  +  2HC1  +  I2. 

TIN,  Sn  (STANNUM). 
Atomic  weight,  117.35;  valence,  II,  IV. 

Bluish-white  metal ;  specific  gravity,  7.29  ;  melting-point, 
235°  C. 

Tin  forms  two  series  of  compounds,  named  respectively 
stannous  and  stannic  compounds.  SnO,  stannous  oxide,  may 
be  taken  as  the  type  of  the  stannous,  and  SnO2  as  the  type 
of  the  stannic  compounds. 


33 


BEHAVIOR   OF   TIN    IN   THE   STANNOUS   CONDITION. 

SnCl2)  stannous  chloride,  may  be  employed  in  making  the 
tests. 

1.  H2S,    hydrogen    sulphide   (also   ammonium    sulphide), 
precipitates  dark-brown  SnS,  stannous  sulphide,  insoluble  in 
colorless  ammonium  sulphide,  but  easily  soluble   in   yellow 
ammonium     sulphide,    witli    the   formation   of   ammonium 
sulphostannatc,  (NH4)2SnS3  : 

SnS  +  (NH4)2S2  =  (NH4)2SnS3. 

From  this  solution  acids  precipitate  yellow  SnS2,  stannic  sul- 
phide : 

(NH4)2SnS3  -f  2HC1  =  SnS2  +  2NH4C1  -f  H2S. 

2.  NaOH,  sodium  hydroxide,  as  well  as  KOH,  potassium 
hydroxide,  precipitates  white  Sn(OH)2,  stannous  hydroxide, 
soluble  in  excess  of  the  reagent.     On  boiling  a  solution  of  a 
stannous  salt  to  which   an  insufficient  quantity  of  sodium  or 
potassium  hydroxide  has  been  added,  the  Sn(OH)2  is  con- 
verted into  black  SnO,  stannous  oxide. 

3.  NH4OH,    ammonium    hydroxide,    precipitates    white 
Sn(OH)2,    stannous   hydroxide,    insoluble   in   excess   of  the 
reagent. 

4.  HgCl2,  mercuric  chloride,  added  to  an  excess  of  SnCl2, 
stannous  chloride,  produces  a  grayish  precipitate  of  finely- 
divided  metallic  mercury  : 


If,  on  the  other  hand,  an  excess  of  mercuric  chloride  is  added 
to  a  stannous  chloride  solution,  a  white  precipitate  of  Hg2Cl2, 
mercurous  chloride,  is  formed  : 

2HgCl2  +  SnCl2=  Hg2Cl2  -f-  SnCl4 

(a  very  delicate  test  and  a  means  of  distinction  between  stan- 
nous and  stannic  salts). 


34 

5.  A  fragment  of  metallic  zinc  placed  in  a  solution  of 
stannous  chloride  precipitates  grayish  metallic  tin  : 

SnCl2  +  Zn  =  ZnCl2-f  Sn. 

If  performed  on  platinum  foil  (see  7  under  Antimony,  page 
31)  the  tin  which  separates  does  not  adhere  to  the  platinum 
foil  as  a  black  coating  (distinction  from  antimony). 

6.  Both  stannous  sails  and  stannic  salts,  when  fused  with 
sodium  carbonate,  or  with  a  mixture  of  sodium  carbonate  and 
potassium  cyanide,  in  the  reducing  flame  on  charcoal,  yield 
white,  ductile  globules  of  metallic  tin  together  with  a  slight 
incrustation  of  SnO2,  stannic  oxide.    Stannic  oxide  moistened 
with  Co(NO3)2,  cobaltous  nitrate,  and  heated  in  the  blowpipe- 
flame  becomes  bluish  green  in  color. 

BEHAVIOR   OF   TIN   IN   THE   STANNIC   CONDITION. 

SnCl4,  stannic   chloride,  may  be  employed  in  making  the 
tests. 

1 .  H2S,  hydrogen  sulphide,  precipitates  yellow  SnS2,  stannic 
sulphide,  insoluble  in  ammonium   carbonate,  but  soluble  in 
colorless  and  also  in  yellow  ammonium  sulphide,  with  the 
formation  of  (NH4)2SnS3,  ammonium  sulphostannate.     From 
this  solution  SnS2  is  reprecipitated  on  the  addition  of  acids. 
SnS2  is  soluble  in  concentrated  hydrochloric  acid. 

2.  NaOH,  sodium  hydroxide,  KOH,  potassium  hydroxide, 
or  NH4OH,  ammonium  hydroxide,  produces  in  solutions  of 
stannic  salts  white  precipitates.     The  precipitate  produced  in 
hydrochloric  acid  solutions  of  ordinary  SnO2,  stannic  oxide,  is 
Sn(OH)4,  stannic  hydroxide,  and  is  easily  soluble  in  dilute 
sodium  or  potassium  hydroxide ;  that  produced  in  solutions 
of  metastannic  acid  is  metastannic  hydroxide,  only  slightly 
soluble  in  excess  of  the  reagent. 

3.  Na2SO4,  sodium  sulphate,  or  ]STH4NO3,  ammonium  ni- 


35 

trate,  in  saturated  solution,  added  in  excess  to  a  hydrochloric 
acid  solution  of  stannic  oxide,  precipitates  the  tin,  particularly 
on  the  application  of  heat,  as  white  Sn(OH)4,  stannic  hydrox- 
ide, or  as  (Sn(OH)4)M,  metastannic  hydroxide  : 
SnCl4  +  4Na2S04  +  4H2O  =  Sn(OH)4  -f-  4NaCl  -j-  4NaHSO4 ; 
SnCl4  +  4NH4NO3  +  4H2O=Sn(OH)4  +  4NH4C1  +  4HNO3. 
(Distinction  from  stannous  salts.) 

4.  Metallic  zinc  reduces  stannic  salts  in  solution  to  metallic 
tin  in  the  same  manner  as  it  reduces  stannous  salts.  (See  5, 
page  34.) 

CADMIUM,  Cd. 
Atomic  weight,  111.7  ;  valence,  II. 

Bluish-white  metal ;  specific  gravity,  8.54 ;  melting-point, 
315°  C. 

CdS04)  cadmium  sulphate,  may  be  employed  in  making  the 

tests. 

1.  H2S,  hydrogen  sulphide,  or  ammonium  sulphide  pro- 
duces a  yellow  precipitate  of  CdS,  cadmium  sulphide,  in- 
soluble in  dilute  acids,  in  ammonium  and  sodium  sulphides, 
and  in  potassium  cyanide,  soluble  in  boiling  nitric  acid,  with 
the  formation  of  Cd(NO3)2,  cadmium  nitrate. 

2.  NaOH,  sodium  hydroxide,  as  well  as  KOH,  potassium 
hydroxide,  precipitates  white  Cd(OH)2,  cadmium  hydroxide, 
insoluble  in  excess  of  the  reagent. 

3.  NH4OH,    ammonium     hydroxide,    precipitates    white 
Cd(OH)2,  cadmium  hydroxide,  soluble  in  excess  of  the  re- 
agent, probably  with  the  formation  of  a  double  salt  of  cad- 
mium and  ammonium,  Cd(ONH4)2. 

4.  KCN,  potassium  cyanide,  added  to  a  neutral  or  ammo- 
niacal  solution  of  a  cadmium  salt,  precipitates  white  Cd(CN)2, 


36 

cadmium  cyanide,  which  is  soluble  in  an  excess  of  potassium 
cyanide,  forming  a  colorless  solution  of  Cd(CN)2(KCN)2 : 

CdS04  +  2KCN  =  Cd(CN)2  +  K2SO4 ; 

Cd(CN)2  +  2KCN  =  Cd(CN)2(KCN)2. 

Hydrogen   sulphide   precipitates   from   this  solution  yellow 
CdS,  cadmium  sulphide. 

5.  Cadmium  compounds,  mixed  with  sodium  carbonate 
and  fused  in  the  reducing  flame  on  charcoal,  yield  yellow  to 
brown  incrustations  of  CdO,  cadmium  oxide. 


GOLD,   Au   (AURUM). 
Atomic  weight,  196.2;   valence,  III. 

Yellow  metal ;  specific  gravity,  19.26 ;  melting-point, 
1035°  C. 

AuCls,  auric  chloride,  may  be  employed  in  making  the  tests. 

1.  H2S,  hydrogen  sulphide,  produces  in  a  cold  solution  of 
auric  chloride  a  black  precipitate  of  AiigSj,  auric  sulphide, 
soluble  in  ammonium  sulphide. 

From  hot  auric  chloride  solutions  hydrogen  sulphide  pre- 
cipitates brownish  metallic  gold  : 

8  AuCls  +  3H2S  +  1 2H2O  =  Au8  +  24HC1  +  3H2SO4. 
2.  NaOH,  sodium  hydroxide,  and  also  potassium  hydrox- 
ide precipitate   reddish-yellow,  amorphous   Au(OH)3,  auric 
hydroxide,  soluble  in  excess  of  the  reagent. 

3.  NH4OH,  ammonium   hydroxide,  produces  a  reddish- 
yellow  precipitate  of  (NH3)2Au2O3,  ammonium  aurate  (fulmi- 
nating gold)  : 

2AuCl3  +  8NH4OH  =  (NHs)2Au2Os  +  6NH4C1  +  5H2O. 

4.  FeSO4,  ferrous  sulphate,  precipitates  in  the  presence  of 
a  free  mineral  acid,  even  in  the  cold,  but  especially  on  heating, 


37 

metallic  gold,  brownish  in  color  because  of  its  finely-divided 
condition  : 

2AuCl3  +  6FeSO4  =  Au2  +  Fe2Cl6  +  2Fe2(SO4)3. 

5.  H2C2O4,  oxalic  acid,  also  precipitates  metallic  gold  from 
auric  chloride  solutions : 

2AuCl3  +  3H2C2O4  =  Au2  +  6HC1  +  6CO2. 
The  precipitation  proceeds  slowly,  but  is  complete.     Warm- 
ing the  solution  facilitates  the  reduction.     The  presence  of 
considerable  free  mineral  acid  interferes  with  the  precipitation. 

6.  SnCl2,  stannous  chloride,  especially  in  very  dilute  solu- 
tion, added  to  auric  chloride  solutions,  produces  a  purplish- 
red  coloration  or  a  purplish-red  precipitate  (purple  of  Cassius), 
consisting  probably  of  a  mixture  of  finely-divided  gold  and 
stannic  oxide. 

7.  Compounds  of  gold   fused  with  sodium  carbonate  or 
with    borax    on    charcoal   yield   yellow,   glistening,   ductile 
spangles  of  metallic  gold. 

PLATINUM,   Pt. 
Atomic  weight,  194.3;  valence,  IV. 

Tin- white  metal ;   specific  gravity,  21.46  ;   melting-point, 
1775°  C. 

platinic  chloride,  may  be  employed  in  making  the 


1.  H2S,  hydrogen  sulphide,  produces  in  cold  platinic  chlo- 
ride solutions  a  brownish  coloration,  but  after  some  time  has 
elapsed  a  brownish-black  precipitate  of  PtS2,  platinic  sulphide, 
separates.     The  precipitate  appears  at  once  on  heating  the 
solution.     The  precipitate  is  insoluble  in  hydrochloric  acid 
and  also  in  nitric  acid,  but  soluble  in  nitro-hydrochloric  acid 
(aqua  regia)  and  also  in  ammonium  sulphide. 

2.  KNO3,  potassium  nitrate,  to  which  a  drop  of  hydro- 

4 


38 

chloric  acid  has  been  added,  or  potassium  chloride,  added  to 
a  concentrated  solution  of  platinic  chloride,  produces  a  yellow, 
crystalline  precipitate  of  (KCl)2PtCl4,  potassium  platinic  chlo- 
ride, slightly  soluble  in  water,  insoluble  in  alcohol.  The  test 
is  best  made  in  a  watch-glass,  the  liquid  being  stirred  with  a 
glass  rod.  Alcohol  facilitates  precipitation. 

3.  NH4C1,  ammonium  chloride,  produces  a  yellow,  crystal- 
line precipitate  of  (NH4Cl)2PtCl4,  ammonium  platinic  chlo- 
ride, slightly  soluble   in  water,  insoluble  in  alcohol.     This 
test  is  best  made  in  a  watch-glass  as  in  2,  above. 

4.  Compounds  of  platinum  heated  in  the  reducing  flame 
are  reduced  to  spongy  metallic  platinum. 


THIRD   GROUP. 

Metals  precipitated  as  hydroxides  by  NH4OH,  ammonium 
hydroxide  :  Iron,  Aluminium,  and  Chromium. 

IRON,   Fe  (FERRUM). 
Atomic  weight,  55.88;  valence,  II,  IV. 

Silver-white  metal ;  specific  gravity,  7.84. 

Iron  forms  two  typical  series  of  compounds,  named  re- 
spectively ferrous  and  ferric  compounds.  FeO,  ferrous  oxide, 
may  be  taken  as  the  type  of  the  ferrous  compounds,  and 
Fe2O3  as  the  type  of  the  ferric  compounds. 

BEHAVIOR   OF    IRON   IN   THE   FERROUS   CONDITION. 

FeSOu  ferrous  sulphate,  may  be  employed  in  making  the 
tests. 

1.  NH4OH,  NaOH,  or  KOH  precipitates,  in  solutions 
of  ferrous  salts  which  are  free  from  dissolved  air,  white 


39 

Fe(OH)2,  ferrous  hydroxide,  which,  by  the  absorption  of 
oxygen,  quickly  changes  in  color  to  green,  black,  and  finally 
to  reddish  brown.  The  presence  of  ammonium  chloride  or 
sulphate  retards  the  precipitation  ;  nevertheless,  in  these  alka- 
line solutions,  in  consequence  of  the  absorption  of  oxygen, 
black  ferrous  hydroxide  and  reddish-brown  ferric  hydroxide 
gradually  separate. 

2.  (NH4)2S  precipitates  black  FeS,  ferrous  sulphide,  insol- 
uble in  excess  of  the  reagent,  easily  soluble  in  hydrochloric 
acid  and  in  nitric  acid.     Very  dilute  ferrous  solutions  are 
colored  green  by  ammonium  sulphide.     Moist  ferrous  sul- 
phide is  oxidized  on  exposure  to  the  air  and  changes  to 
reddish-brown  Fe2O(SO4)2,  basic  ferric  sulphate. 

3.  K4Fe(CN)6,  potassium  ferrocyanide,  produces  in  ferrous 
solutions  free  from    ferric   salts  a  white  precipitate,  which 
quickly  changes  to  bluish-white  K2Fe(Fe(CN)6),  potassium 
ferrous  ferrocyanide  (Everett's  salt),  insoluble  in  acids.     On 
exposure  to  air  the  bluish-white  precipitate  gradually  absorbs 
oxygen  and  changes  to  blue  Fe4(Fe(CN)6)3,  ferric  ferrocyanide 
(Prussian  blue) : 

4K2Fe(Fe(CN)6)  +  O2  +  4HC1  =  Fe4(Fe(CN)6)3  + 
K4Fe(CN)6  +  4KC1  +  2H2O. 

4.  K3Fe(CN)6,  potassium   ferricyanide,  precipitates  dark- 
blue  Fe3(Fe(CN)6)2,   ferrous   ferricyanide  (Turnbull's  blue), 
insoluble  in  acids. 

5.  KCNS,  potassium  sulphocyanide,  does  not  produce  a 
claret-red  coloration  in  solutions  of  ferrous  salts  free  from 
ferric  salts.     (Distinction  from  ferric  salts.) 

6.  Ferrous  compounds  and  also  ferric  compounds  when 
ignited  with    sodium   carbonate  on  charcoal  yield  a  black 
magnetic  oxide. 

7.  All  compounds  of  iron  when   fused  in  the  oxidizing 
flame  in  a  bead  of  borax  yield  while  hot  a  yellow  or  reddish- 


40 

brown  bead,  which  on  cooling  becomes  lighter  in  color  or 
colorless.  Fused  in  the  reducing  flame  the  bead  becomes 
bottle-green  in  color. 

BEHAVIOR   OF   IRON    IN   THE    FERRIC   CONDITION. 

Fe^Clgj  ferric  chloride,  may  be  employed  in  making  the  tests. 

1.  NH4OH,   NaOH,  or  KOH  produces  in  solutions  of 
ferric    salts    a    voluminous,    reddish-brown    precipitate    of 
Fe.j(OH)6,  ferric  hydroxide,  insoluble  in  excess  of  the  reagent 
and  in  ammonium  salts. 

2.  (NHJgS  precipitates  black  FeS  together  with  free  sul- 
phur : 

Fe2Cl6  +  3(NH4)2S  —  2FeS  +  S  +  6NH4C1. 

3.  K4Fe(CN)6,  potassium  ferrocyanide,  precipitates,  even 
in     exceedingly     dilute     solutions     of     ferric     salts,     blue 
Fe4(Fe(CN)6)3,  ferric  ferrocyanide  (Prussian  blue),  insoluble 
in  acids,  but  decomposed  by  alkalies. 

4.  K3Fe(CN)6,  potassium  ferricyanide,  does  not  produce  a 
precipitate  in  ferric  solutions,  but  imparts  a  green  or  brown 
coloration  to  the  solution.     (See  3,  page  80.) 

5.  KCNS,  potassium  sulphocyanide,  produces  an  intense 
claret-red  coloration  in  ferric  solutions,  due  to  the  formation 
of  soluble  Fe2(CNS)6,  ferric  sulphocyanide.     In  exceedingly 
dilute  solutions  the  color  is  pale  red.     HgCl2,  mercuric  chlo- 
ride, destroys  the  coloration,  soluble  Hg(CNS)2  being  formed. 

6.  NaC2H3O2,  sodium  acetate,  added  to  a  ferric  salt  colors 
the  solution  dark  red,  due  to  the  formation  of  Fe2(C2H3O2)6, 
ferric  acetate,  which,  on  boiling  the  sufficiently  diluted  solu- 
tion, separates  with  part  of  the  acetic  acid  as  a  brownish- 
red,  flocculent  precipitate  of  Fe2(OH)4(C2H3O2)2,  basic  ferric 
acetate : 

A)e  +  4H20  =  Fc2(OH)<(C2H302\  +  4HC2H3O8. 


41 

7.  H2S,  hydrogen  sulphide,  reduces  ferric  salts  in  solution 
to  ferrous  salts,  with  the  separation  of  sulphur : 

Fe2Cl6  +  H2S  =  2FeCl2  +  2HC1  +  S. 

8.  For  the  behavior  of  ferric  salts  on  charcoal  and  in  the 
borax  bead  see  under  Ferrous  Salts,  7,  page  39. 

ALUMINIUM,    Al. 
Atomic  weight,  27, 04;  valence,  IV. 

Tin-white  metal ;  specific  gravity,  2.56  (spec.  grav.  of  the 
hammered  metal  2.67) ;  melting-point,  about  700°  C. 

Al2(804\j  aluminium  sulphate,  or  NH^Al(80^  ammonium 
aluminium  sulphate  (ammonia  alum),  may  be  employed  in 
making  the  tests. 

1 .  NH4OH  precipitates  white,  gelatinous  A12(OH)6,  alumin- 
ium hydroxide,  slightly  soluble  in  an  excess  of  the  reagent. 
The  precipitation  is  complete  only  when  the  excess  of  am- 
monia has  been  driven  off  by  boiling  the  solution. 

2.  NaOH    or    KOH   precipitates    gelatinous    A12(OH)6, 
aluminium  hydroxide,  soluble  in  an  excess  of  either  reagent, 
with    the  formation  of  Al2O2(ONa)2,  sodium   aluminate,  or 
A12O2(OK)2  potassium  aluminate : 

A12(OH)6  -f  2NaOH  =  Al2O2(ONa)2  +  4H2O. 
As  aluminium  hydroxide  is  insoluble  in  ammonium  hydrox- 
ide (providing  the  latter  is  not  present  in  great  excess),  the 
aluminium  hydroxide  may  be  reprecipitated  from  its  solution 
as  aluminate  by  the  addition  of  ammonium  chloride : 
Al202(ONa)2+ 2NH4C1  +  2H2O= A12(OH)6+  2NH8+2NaCl. 
Boiling  does  not  decompose  the  aluminates.     The  solutions 
of  aluminates  have  an  alkaline  reaction. 

3.  (NH4)2S  completely  precipitates  aluminium  from  its  solu- 
tion as  A12(OH)6,  aluminium  hydroxide,  with  the  evolution 
of  hydrogen  sulphide. 


42 

4.  N^HPO^  sodium  hydrogen  phosphate,  precipitates  in 
neutral  solutions  white  gelatinous  A12(PO4)2,  aluminium  phos- 
phate, insoluble  in  acetic  acid  and  in  ammonium  hydrox- 
ide, soluble  in  mineral  acids  and  in  sodium  or  potassium 
hydroxide,  with  the  formation  of  alumi  nates  : 

A12(PO4)2  +  SNaOH  =  Al2O2(ONa)2  +  2Na3PO4  +  4H2O. 
Ammonium  chloride  reprecipitates  the  aluminium  phosphate 
from  its  solution  in  sodium  or  potassium  hydroxide  : 

Al2O2(ONa)2  -f-  2Xa3PO4  +  8NH4C1  ==  A12(PO4)2  +  SNaCl 
+  8NH3  +  4H2O. 

5.  Na^Og,  sodium  hyposulphite,  added  to  a  neutral  solu- 
tion of  a   salt  of  aluminium   precipitates  white,  gelatinous 
A12(OH)6,  with  the  separation  of  free  sulphur  and  libera- 
tion of  SO2,  sulphurous  anhydride.     Complete  precipitation 
takes  place  only  when  the  solution  of  the  aluminium  salt  is 
dilute  and  is  boiled,  after  the  addition  of  the  hyposulphite, 
until  the  odor  of  sulphurous  anhydride  can  no  longer  be 
detected  : 

A12C16  +  SNaAOs  +  3H2O  =  A12(OH)6  +  6NaCl  +  3SO2 


6.  Compounds  of  aluminium,  mixed  with  sodium  carbon- 
ate and  ignited  on  charcoal,  yield  white,  infusible  aluminium 
oxide  ;  on  moistening  the  mass  with  cobaltous  nitrate  and 
again  igniting,  an  infusible  blue  residue  is  obtained,  due  to 
the  combination  of  CoO,  cobaltous  oxide,  with  A12O3,  alumin- 
ium oxide  (Thenard's  blue). 

CHROMIUM,  Cr. 

Atomic  weight,  52.45;  valence,  II,  IV. 
Light-gray,  crystalline  powder;  specific  gravity,  6.81. 
O2C76,  chromic  chloride,  may  be  employed  in  making  the  tests. 
1.  NH4OH  precipitates  bluish-gray,  gelatinous  Cr2(OH)6, 


43 

chromic  hydroxide ;  if  the  precipitation  has  taken  place  in  a 
cold  solution,  a  small  quantity  of  chromic  oxide  will  remain 
dissolved  in  the  ammonium  hydroxide ;  on  boiling  this  pink- 
ish solution  all  of  the  chromium  is  precipitated  as  chromic 
hydroxide. 

2.  XaOH  or  KOH  precipitates  from  solutions  of  both  the 
green  and  the  violet  salts  of  chromium  greenish,  flocculent 
Cr2(OH)6,  chromic   hydroxide,  soluble   in  an  excess  of  the 
reagent,  forming  Cr2O2(ONa)2,  sodium  chromite,  and  impart- 
ing a  greenish  color  to  the  solution  : 

O2(OH)6  +  2NaOH  =  Cr2O2(ONa)2  +  4H2O. 
From  this  solution  chromic  hydroxide  is  reprecipitated  by  the 
addition  of  ammonium  chloride  or  by  long-continued  boiling : 

O2Oa(ONa)a  4.  4H2O  ==  Cr2(OH)6  +  2NaOH. 
The  precipitated  chromic  hydroxide  obtained  by  boiling  its 
alkaline  solution  appears  to  be  insoluble  in  sodium  or  potas- 
sium hydroxide.  It  is  probably  a  chromic  hydroxide  some- 
what deficient  in  water  of  hydration.  The  solubility  of 
chromic  hydroxide  in  sodium  hydroxide  is  very  much  re- 
tarded by  the  presence  of  ferric  oxide. 

3.  (NH4)2S  precipitates  Cr2(OH)6,  chromic  hydroxide,  with 
the  evolution  of  hydrogen  sulphide  : 

Cr2Cl6  +  3(NH4)2S  +  6H2O  -  Cr2(OH)6  +  6NH4C1  +  3H2S. 

4.  A  salt  of   chromium,   fused  on  platinum  foil  with  a 
mixture  of  sodium  carbonate  and  potassium  nitrate  or  potas- 
sium chlorate,  yields  a  mass  containing  a  salt  of  chromic 
acid, — i.e.,  a  chromate  ;  on  exhausting  the  mass  with  water  a 
yellow  solution  of  Na2CrO4,  sodium  chromate,  or  K2CrO4, 
potassium  chromate,  is  obtained,  which  when  treated  with 
plumbic  acetate  yields  a  yellow  precipitate  of  PbCrO4,  plumbic 
chromate : 

O2O3  +  2Na2CO3  +  O3  =  2Na2CrO4  +  2CO2 ; 

Pb(C2H3O2)2  =  PbCrO4  +  2NaC2H3O2. 


44 

5.  Compounds  of  chromium  when  ignited  with  sodium  car- 
bonate on  charcoal  yield  a  green  fused  mass  containing  oxides 
of  chromium. 

6.  Fused  in  a  bead  of  borax  or  of  microcosmic  salt,  in 
either  the  oxidizing  or  the  reducing  flame,  chromium  com- 
pounds yield  a  yellowish-green  bead,  which  becomes  emerald- 
green  on  cooling. 


FOURTH   GROUP. 

Metals  precipitated  as  sulphides  from  neutral  solutions  by 
(NH4)2S,  ammonium  sulphide :  Manganese,  Zinc,  Cobalt,  and 
Nickel. 

MANGANESE,   Mn. 

Atomic  weight,  54.8;   valence,  II,  IV. 
Grayish- white  metal ;  specific  gravity,  about  8. 

MnSO±,  manganous  sulphate,  may  be  employed  in  making 
the  tests. 

1.  (NH4)2S  precipitates  pale-salmon-colored  MnS,  manga- 
nous  sulphide,  containing  water,  easily  soluble  in  acetic  acid 
and   in   hydrochloric   acid.      (Occasionally,    especially   after 
standing  some  time,  the  pale-salmon-colored  precipitate  con- 
taining water  is  converted  into  green  MnS,  manganous  sul- 
phide,   which   is   free   from   water.)      Manganous   sulphide 
readily  oxidizes  on  exposure  to  the  air  and  becomes  dark 
brown,  due  to  the  formation  of  MnO(OH)2,  hydrated  peroxide 
of  manganese. 

2.  NaOH  or  KOH  precipitates  white  Mn(OH)2,  manganous 
hydroxide,  insoluble  in  excess  of  the  reagent.     On  exposure 
to  the  air  the  precipitate  rapidly  becomes  brown,  due  to  the 


45 

formation  of  Mn2(OH)6,  manganic  hydroxide.  Manganous 
hydroxide  is  soluble  in  ammonium  chloride,  owing  to  the 
production  of  a  double  salt,  whereas  manganic  hydroxide  is 
insoluble  in  that  reagent ;  on  this  account  ammonium  chloride 
solutions  of  manganous  hydroxide  containing  free  ammonia 
become  brown  on  exposure  to  the  air,  due  to  the  separation 
of  manganic  hydroxide : 

Mn(OH)2  -f  4NH4C1  =  MnCl2(NH4Cl)2  -j-  2H2O  +  2NH3 ; 
2MnCl2(NH4Cl)2  +  4NH3  +  5H2O  +  O  =  Mn2(OH)6  + 

8NH4C1. 

3.  NH4OH  precipitates  in  neutral  solutions,  and  also  in 
solutions  free  from  salts    of  ammonium,  white  Mn(OH)2, 
manganous  hydroxide;  in  the  presence  of  salts  of  ammonium 
or  of  free  acids,  excess  of  ammonium  hydroxide  fails  to  pro- 
duce a  precipitate,  because  of  the  formation  of  a  soluble 
double  salt  of   manganous  hydroxide  with  the  ammonium 
salts.     The  action  of  the  oxygen  of  the  air  converts  the  solu- 
ble manganous   salt    into   Mn2(OH)6,   manganic  hydroxide, 
which  separates  as  a  brown  precipitate. 

4.  Compounds  of  manganese,  fused  on  platinum  foil  with 
sodium  carbonate  and  potassium  nitrate,  yield  a  bluish-green 
mass  containing  manganates  of  sodium  and  potassium : 
3Mn(OH)2  -f-  Na2CO3  +  4KNO3  =  Na2MnO4  +  2K2MnO4  + 

4NO  +  CO2  +  3H2O. 

The  test  is  an  exceedingly  delicate  one,  and  only  a  minute 
quantity  of  a  salt  of  manganese  need  be  used. 

On  exhausting  the  mass  with  water,  soluble  KMnO4, 
potassium  permanganate,  and  insoluble  brown  MnO(OH)9, 
hydrated  peroxide  of  manganese,  are  formed : 

3K2MnO4  +  3H2O  =  2KMnO4  -f  MnO(OH)2  +  4KOH. 
The  potassium  permanganate  dissolves,  imparting  a  purplish- 
red  color  to  the  water. 

5.  Compounds  of  manganese,  fused  in  the  oxidizing  flame 


46 

in  a  bead  of  borax  or  of  microcosmic  salt,  yield  an  amethyst- 
colored  bead ;  fused  in  the  reducing  flame,  the  bead  becomes 
colorless. 

ZINC,   Zn. 
Atomic  weight,  64.88;  valence,  II. 

Bluish-white  metal ;  specific  gravity,  6.9 ;    melting-point, 
433°  C. 

ZnS04,  zinc  sulphate,  may  be  employed  in  making  the  tests. 

1.  (NH4)2S  precipitates  white  ZnS,  zinc  sulphide,  easily 
soluble  in  hydrochloric  acid,  insoluble  in  acetic  acid. 

2.  NaOH  or  KOH  precipitates  white,  gelatinous  Zn(OH)2, 
zinc  hydroxide,  soluble  in  excess  of  the  reagent,  with  the 
formation  of  Zn(ONa)2,  sodium  zincate,  or  Zn(OK,2,  potas- 
sium zincate : 

Zn(OH)2  -f  2NaOH  =  Zn(ONa)2  +  2H2O. 
These   solutions,  which  have  an  alkaline   reaction,  yield  a 
precipitate  of  ZnS,  zinc  sulphide,  on  the  addition  of  hydrogen 
sulphide. 

3.  NH4OH  precipitates  in  neutral  solutions  white,  floccu- 
lent  Zn(OH)2,  zinc  hydroxide,  soluble  in  excess  of  the  reagent. 

4.  K4Fe(CN)6,  potassium  ferrocyanide,  produces  a  white, 
flocculent  precipitate  of  Zn2Fe(CN)6,  zinc  ferrocyanide,  in- 
soluble in  acids  and  in  ammonium  hydroxide.     The  precipi- 
tate while  in  suspension  often  has  a  pale-yellowish  appear- 
ance, due  to  the  color  imparted  to  the  liquid  by  the  presence 
of  an  excess  of  potassium  ferrocyanide. 

5.  Compounds  of  zinc,  ignited  with  sodium  carbonate  in 
the  reducing  flame  on  charcoal,  yield  a  coating  of  ZnO,  zinc 
oxide,  which  is  yellow  when  hot  and  white  when  cold.     On 
moistening  the  deposit  with  cobaltous  nitrate  and  again  ignit- 
ing, the  deposit  becomes  green  in  color. 


47 


COBALT,  Co. 
Atomic  weight,  58.6;  valence,  II,  IV. 

Steel-gray  metal ;  specific  gravity,  8.6. 

Co(N03)2,  cobaltous   nitrate,  or   CoCl2,   cobaltous  chloride, 
may  be  employed  in  making  the  tests. 

1.  (NH4)2S  precipitates  black  CoS,  cobalt  sulphide,  insolu- 
ble in  excess  of  colorless  ammonium  sulphide  and  in  dilute 
hydrochloric  acid;  soluble  in  nitro-hydrochloric  acid,  with 
the  formation  of  CoCl2,  cobaltous  chloride : 

3CoS  +  6HC1  -j-  2HNO3  =  3CoCl2  +  S3  +  2NO  +  4H2O. 

2.  NaOH  or  KOH  precipitates  in  cold  cobaltous  solu- 
tions a  bluish  basic  salt,  and  in  boiling  solutions  rose-red 
Co(OH)2,  cobaltous  hydroxide.      Both  precipitates  become 
oxidized  on  exposure  to  the  air  and  turn  olive-green  in  color. 
They  are  insoluble  in  excess  of  the  reagent. 

3.  NH4OH  precipitates  in  cold  cobaltous  solutions  a  bluish 
basic  salt,  and  in  boiling  solutions  rose-red  Co(OH)2,  cobalt- 
ous hydroxide.     Both  of  these  precipitates  are  soluble  in  an 
excess  of  the  reagent,  imparting  a  reddish  color  to  the  liquid, 
which,  on  exposure  to  the  oxidizing  action  of  the  air,  soon 
changes  to  brown. 

4.  KCN,  potassium  cyanide,  precipitates   brownish-white 
Co(CN)2,  cobaltous  cyanide,  soluble  in  excess  of  the  reagent, 
with  the  formation  of  (KCN)2Co(CN)2,  potassium  cobaltous 
cyanide,  from  which  solution  cobaltous  cyanide  is  reprecipi- 
tated  by  hydrochloric  acid. 

5.  KNO2,  potassium  nitrite,  added  in  excess  to  a  somewhat 
concentrated  solution  of  a  salt  of  cobalt,  to  which  sufficient 
acetic  acid   has  previously  been  added,  produces  a  yellow', 
crystalline  precipitate  of   K6Co2(]S"O2)12,  potassium   cobaltic 
nitrite  =  (KNO2)6Co2(NO2)6 : 


48 

2CoCl2  +  14KN02  +  4HC2H302  -  K6Co2(NO2)12  + 

4KC2H3O2  +  4KC1  +  2NO  +  2H2O. 

In  concentrated  cobalt  solutions  the  precipitate  appears  im- 
mediately, while  in  dilute  solutions  it  requires  some  time  for 
it  to  form. 

The  presence  of  free  acetic  acid  is  necessary  to  liberate  the 
nitrous  acid  (required  in  the  oxidation)  from  the  potassium 
nitrite.  Free  hydrochloric  acid  must  not  be  present ;  in  case 
of  its  presence  in  the  solution,  it  must  be  neutralized  by  the 
addition  of  NaC2H3O2,  sodium  acetate,  previous  to  the  addi- 
tion of  the  acetic  acid.  To  insure  complete  precipitation  of 
the  cobalt,  particularly  in  the  case  of  dilute  solutions,  the  so- 
lution should  be  allowed  to  stand  in  a  warm  place  for  about 
twenty-four  hours. 

6.  Compounds  of  cobalt,  ignited  -with  sodium  carbonate  in 
the  reducing  flame  on  charcoal,  yield  dark,  metallic,  magnetic 
spangles. 

7.  Compounds  of  cobalt,  fused  in  a  bead  of  borax  or  of 
microcosmic  salt  in  either  the  reducing  or  the  oxidizing  flame, 
impart  to  the  bead  a  beautiful  sapphire-blue  color. 

NICKEL,  Ni. 

Atomic  weight,  58.6;  valence,  II,  IV. 
Silver- white  metal ;  specific  gravity,  8.9. 

NiSOt,  nickelous  sulphate,  or  NiCl2,  nickelous  chloride,  may 
be  employed  in  making  the  tests. 

1.  (NH4)2S  precipitates  black  NiS,  nickelous  sulphide,  sol- 
uble in  excess  of  ammonium  sulphide  (particularly  in  the 
presence  of  ammonia),  imparting  a  brownish  color  to  the 
solution.  On  boiling  the  ammonium  sulphide  solution  of 
nickelous  sulphide,  it  undergoes  decomposition  (particularly 


49 

after  the  addition  of  acetic  acid),  with  the  separation  of  the 
dissolved  nickclous  sulphide.  The  precipitate  is  insoluble  in 
dilute  hydrochloric  acid,  but  soluble  in  nitre-hydrochloric 
acid. 

2.  NaOH  or  KOH  precipitates  amorphous,  apple-green 
Ni(OH)s,  nickelous  hydroxide,  insoluble  in  an  excess  of  the 
reagent. 

3.  NH4OH,  added  in  small  quantity,  precipitates,  in  neu- 
tral solutions  of  nickelous  salts  free  from  ammonium  salts, 
apple-green  Ni(OH)2,  nickelous  hydroxide,  soluble  in  excess 
of  ammonium   hydroxide,  imparting  a  bluish  color  to  the 
solution. 

4.  KCN,    potassium     cyanide,    precipitates     light-green 
Ni(ON)j,    nickelous    cyanide,    soluble  in  excess   of  the   re- 
agent,   with   the   formation   of  (KCN)2Ni(CN)2,   potassium 
nickelous  cyanide.    Hydrochloric  acid  reprecipitates  from  this 
solution  Ni(CN)2,  nickelous  cyanide.     (Distinction  from  co- 
balt.) 

5.  KNO2,  potassium  nitrite  (under  the  conditions  given 
for  cobalt,  5,  page  47),  fails  to  produce  a  precipitate  in  solu- 
tions of  nickelous  compounds. 

6.  Compounds  of  nickel,  ignited  with  sodium  carbonate 
on  charcoal,  yield  dark,  magnetic,  metallic  spangles. 

7.  Compounds  of  nickel,  fused  in  the  oxidizing  flame  in  a 
bead  of  borax,  yield  a  bead  which  is  purplish  red  while  hot 
and  pale  brownish  yellow  when  cold.     In  the  reducing  flame 
the  bead  becomes  gray  and  opaque,  due  to  the  separation  of 
metallic  nickel. 

Fused  in  a  bead  of  microcosmic  salt  in  the  oxidizing  or 
the  reducing  flame,  salts  of  nickel  yield  a  reddish-brown  bead 
which  becomes  yellow  or  yellowish  red  on  cooling. 


50 


FIFTH   GROUP. 

Metals  precipitated  as  carbonates  from  neutral  solutions  by 
(NH4)2CO3,  ammonium  carbonate :  Barium,  Strontium,  and 
Calcium. 

Complete  precipitation  does  not  take  place  in  solutions 
which  were  originally  acid,  or  when  ordinary  commercial  am- 
monium carbonate  is  employed,  unless  the  solution  is  boiled 
after  the  addition  of  the  ammonium  carbonate.  Commer- 
cial ammonium  carbonate  consists  of  equal  molecules  of 
NH4HCO3,  acid  ammonium  carbonate,  and  NH4NH2COO, 
ammonium  carbamate.(1)  Dissolving  the  commercial  carbonate 
in  water  converts  the  ammonium  carbamate  into  neutral 
ammonium  carbonate : 

NH4HC03  +  NH4NH2COO  +  H2O  =  NH4HCO3  + 

(NH4)2C03. 

In  precipitating  with  ammonium  carbonate  containing  acid 
ammonium  carbonate,  part  of  the  precipitate  will  consist  of 
acid  salts, — for  example,  J>a(HCO3)2, — which  are  converted 
into  neutral  salts  on  boiling : 

Ba(HCO3)2  =  BaCO3  +  CO2  -f  H2O. 

BARIUM,   Ba. 

Atomic  weight,  136.86;  valence,  II. 
Silver-white  metal ;  specific  gravity,  about  4.0. 

BaCl2j  barium  chloride,  may  be  employed  in  making  the 
tests. 

1.  (NH4)2CO3,   ammonium    carbonate,  precipitates  white, 

1  According  to  other  views,  commercial  ammonium  carbonate  consists 
of  one  molecule  of  neutral  and  two  molecules  of  acid  ammonium  carbon- 
ate, thus : 

(NH4)2CO3  +  2NH4HCO3 


51 

flocculent  BaCO3,  barium  carbonate.  The  precipitate  is 
easily  soluble  in  dilute  hydrochloric  acid,  in  nitric  acid,  and 
in  acetic  acid,  insoluble  in  pure  water,  slightly  soluble  in 
ammonium  chloride,  and,  like  all  the  carbonates  of  the  alka- 
line earths,  soluble  in  water  containing  carbonic  acid. 

2.  H2SO4,  sulphuric  acid,  and  soluble  sulphates,  including 
solutions   of   calcium   and   strontium    sulphates,    precipitate 
white,  finely-pulverulent  BaSO4,  barium  sulphate,  insoluble 
in  acids.     If  the  precipitation  occur  in  a  cold  solution,  the 
particles  of  the  precipitate  are  so  minute  that  they  readily 
pass  through  a  filter ;  whereas,  if  the  precipitation  take  place 
in  a  hot  solution,  the  precipitate  that  is  formed  is  crystalline 
and  readily  retained  by  a  filter. 

3.  (NH4)2C2O4,  ammonium  oxalate,  precipitates  white,  pul- 
verulent BaC2O4,  barium  oxalate,  which  when  freshly  precip- 
itated is  soluble  in  acetic  acid  and  in  H2C2O4,  oxalic  acid. 

4.  Na2HPO4,    sodium    hydrogen   phosphate,    precipitates 
white,  flocculent  BaHPO4,  di-basic  barium  phosphate,  soluble 
in  hydrochloric,  nitric,  and  acetic  acids. 

5.  K2CrO4,  potassium  chromate,  produces  in  neutral   or 
acetic  acid  solutions  of  salts  of  barium  yellow  BaCrO4,  barium 
chromate,  soluble  in  hydrochloric  acid  and  in  nitric  acid. 

6.  Compounds  of  barium,  held  in  the  flame  of  a  Bunsen 
burner  by  means  of  a  platinum  wire,  impart  a  yellowish- 
green  color  to  the  flame. 

STRONTIUM,    Sr. 
Atomic  weight,  87.3;   valence,  II. 
Yellowish  metal ;  specific  gravity,  2.5. 
$r(JV03)2,  strontium  nitrate,  may  be  employed  in  making  the 


1.    (NH4)2CO3,  ammonium   carbonate,   precipitates   white 


52 

SrCO3,  strontium  carbonate,  easily  soluble  in  dilute  hydro- 
chloric acid,  in  nitric  acid,  and  in  acetic  acid. 

2.  H2SO4,  sulphuric  acid,  and  soluble  sulphates,  including 
calcium  sulphate,  precipitate  white,  usually  crystalline  SrSO4, 
strontium  sulphate,  insoluble  in  alcohol.     In  dilute  solutions, 
and  also  on  using  calcium  sulphate  as  the  precipitating  re- 
agent, the  precipitation  takes  place  gradually. 

3.  (NH4)2C2O4,    ammonium    oxalate,    precipitates   white, 
pulverulent  SrC2O4,  strontium  oxalate,  soluble  Avith  difficulty 
in  acetic  acid  and  in  oxalic  acid. 

4.  Na^HPO^     sodium     phosphate,     precipitates     white 
SrHPO4,  di-basic  strontium   phosphate,   soluble  in   hydro- 
chloric, nitric,  and  acetic  acids. 

5.  K2CrO4,  potassium  chromate,  does  not  produce  a  pre- 
cipitate with  salts  of  strontium. 

6.  Compounds  of  strontium  impart  a  crimson  color  to  the 
flame. 

CALCIUM,  Ca. 

Atomic  weight,  39.9;  valence,  II. 
Yellowish  metal ;  specific  gravity,  1.57. 
CdCl2j  calcium  chloride,  may  be  employed  in  making  the  tests. 

1.  (NH4)2CO3,   ammonium    carbonate,    precipitates    white 
CaCO3,  calcium  carbonate,  easily  soluble  in   dilute   hydro- 
chloric acid,  in  nitric  acid,  and  in  acetic  acid. 

2.  H2SO4  and  soluble  sulphates  precipitate  immediately,  in 
concentrated  solutions  of  salts  of  calcium,  white,  crystalline 
CaSO4,  calcium  sulphate,  insoluble  in  alcohol,  but  soluble  in 
boiling  hydrochloric  acid.     Precipitation  takes  place  in  dilute 
solutions  either  gradually  or  not  at  all. 

3.  (NH4)2C2O4,  ammonium  oxalate,  precipitates  white,  pul- 


53 

verulent  CaC2O4,  calcium  oxalate,  easily  soluble  in  hydro- 
chloric or  in  nitric  acid,  insoluble  in  acetic  and  oxalic  acids. 

4.  Na2HPO4,    sodium    hydrogen    phosphate,    precipitates 
white  CaHPO4,  di-basic  calcium  phosphate,  soluble  in  hydro- 
chloric, nitric,  and  acetic  acids. 

5.  K2CrO4,  potassium  chromate,.  does  not  produce  a  pre- 
cipitate in  solutions  of  calcium  salts. 

6.  Compounds  of  calcium  impart  a  yellowish-red  color  to 
the  flame. 


SIXTH  GROUP. 

Bases  not  precipitated  by  any  particular  group  reagent: 
Magnesium,  Potassium,  Sodium,  Ammonium,  and  Lithium. 

MAGNESIUM,   Mg. 
Atomic  weight,  23.94;   valence-  II. 
Silver- white  metal ;  specific  gravity,  1.75. 

MgSOu  magnesium  sulphate,  may  be  employed  in  making 
the  tests. 

1.  NH4OH  precipitates,  in  neutral  solutions  of  salts  of 
magnesium,  part  of  the  magnesium  as  flocculent  Mg(OH)2, 
magnesium  hydroxide,  leaving  the  other  part  in  solution  as  a 
double  salt  of  magnesium  and  ammonium : 

2MgSO4  +  2NH4OH  =  Mg(OH)2  +  MgSO4(NH4)2SO4. 
This  double  salt  is  not  decomposed  by  a  slight  excess  of 
ammonium  hydroxide.  Compounds  of  magnesium  are  not 
precipitated  by  ammonium  hydroxide  in  the  presence  of  an 
excess  of  ammonium  chloride,  the  latter  reagent  having  the 
property  of  dissolving  magnesium  hydroxide : 

Mg(OH)2  +  4NH4C1  =  MgCl2(NH4Cl)2  +  2NH4OH. 


54 
. 

2.  NaOH  or  KOH  precipitates,  particularly  on  boiling, 

white  Mg(OH)2,  magnesium  hydroxide. 

3.  NagCOg,  sodium  carbonate,  or  K2CO3,  potassium  car- 
bonate, precipitates  Mg4(CO3)3(OH)2,  basic  magnesium  car- 
bonate.    (The  carbonic  acid  liberated  in  the  reaction  retains 
part  of  the  magnesium  in  solution  as  an  acid  carbonate ;  this 
is  precipitated  by  boiling  the  solution.)     The  precipitate  is 
soluble  in  ammonium  chloride. 

4.  (NH4)2CO3     produces     no     precipitate     immediately, 
but  after   standing   some   time   a  crystalline  precipitate  of 
MgCO3(NH4)2CO3  appears.     In  the  presence  of  a  sufficient 
quantity  of  ammonium  chloride  the  precipitation  does  not 
take  place. 

o.  Na2HPO4  produces  in  concentrated  solutions  a  white, 
flocculent  precipitate  of  MgHPO4,  di-basic  magnesium  phos- 
phate. If  ammonium  chloride  and  ammonium  hydroxide 
are  added  to  the  solution  of  the  magnesium  salt,  and  after- 
wards sodium  hydrogen  phosphate  added,  a  white,  crystalline 
precipitate  of  MgNH4PO4,  ammonium  magnesium  phosphate, 
is  produced : 
MgSO4  -f  Na2HPO4  +  NH4OH  =  MgNH4PO4  +  Na2SO4  + 

H20. 

The  ammonium  chloride  is  added  to  the  solution  in  order  to 
prevent  the  precipitation  of  the  magnesium  salt  by  the  am- 
monium hydroxide.  The  precipitate  is  always  crystalline; 
in  dilute  solutions  it  forms  gradually,  the  formation  is  facili- 
tated, however,  by  gently  rubbing  the  inner  sides  of  the 
vessel  with  a  glass  rod. 

6.  Compounds  of  magnesium  ignited  on  charcoal  are  some- 
what luminous  in  the  flame.  On  moistening  the  mass  with 
cobaltous  nitrate  and  again  strongly  igniting,  a  pale-pink 
color,  which  is  more  evident  on  cooling,  is  imparted  to  the 
mass. 


55 

POTASSIUM,  K  (KALIUM). 
Atomic  weight,  39.O3  ;    valence,  I. 

Silver- white  metal ;  specific  gravity,  0.87  ;  melting-point, 
62.5°  C. 

KN03,  potassium  nitrate,  or  KCl,  potassium  chloride,  may 
be  employed  in  making  the  tests. 

1.  PtCl4,  platinic  chloride,  precipitates  from  neutral  or  acid 
solutions  yellow,  crystalline  (KCl)2PtCl4,  potassium  platinic 
chloride,  slightly  soluble  in  water,  insoluble  in  alcohol.     The 
test  is  best  made  in  a  watch-glass,  and  the  liquid  should  be 
stirred  with  a  glass  rod.     In  dilute  solutions  the  precipitate 
forms  slowly.     The  addition  of  a  little  alcohol  and,  if  the 
potassium  salt  is  not  a  chloride,  a  drop  of  hydrochloric  acid 
facilitates  the  precipitation. 

2.  NaHC4H4O6,  acid  sodium  tartrate,  produces,  in  rather 
concentrated  neutral  solutions  of  salts  of  potassium,  a  white, 
granular,  crystalline  precipitate  of  KHC4H4O6,  acid  potas- 
sium tartrate.     Stirring  the  liquid  with  a  glass  rod  or  the 
addition  of  alcohol  promotes  the  precipitation.     If  the  po- 
tassium solution  has  an  alkaline  reaction,  it  must  be  neutral- 
ized with  acetic  acid  previous  to  the  addition  of  the  acid  so- 
dium tartrate.     H2C4H4O6,  tartaric  acid,  may  be  used  instead 
of  acid  sodium  tartrate,  but  in  using  it  NaC2H3O2,  sodium 
acetate,  must  be  added  to  the  solution  : 

KN03  +  H2C4H406  +  NaC2H302  =  KHC4H4O6  +  NaNOs  + 

HC2H3O2. 

In  dilute  solutions  of  potassium  salts  precipitation  occurs 
only  after  standing  some  time. 

3.  Compounds  of  potassium  impart  to  the  flame  a  violet 
color, 


56 

SODIUM,  Na   (NATRIUM). 
Atomic  weight,  22.99;   valence,  I. 

Silver-white  metal;  specific  gravity,  0.97;  melting-point, 
95.6°  C. 

NaCly  sodium  chloride,  may  be  employed  in  making  the  tests. 

1.  K2H2Sb2O7,    potassium    pyroantimonate,    produces,    in 
neutral  or  slightly  alkaline  concentrated  solutions  of  salts 
of  sodium,  a  white,  crystalline  precipitate  of  Na2H2Sb2O7, 
sodium  pyroantimonate.     In  dilute  solutions  the  precipitate 
forms  only  after  the  liquid  has  been   standing  some  time. 
Gently  rubbing  the  inner  sides  of  the  vessel  facilitates  the 
formation  of  the  precipitate.     If  the  sodium  solution  have 
an  acid  reaction,  it  must  be  neutralized  with  potassium  car- 
bonate before  the  addition  of  the  potassium  pyroantimonate. 
Metals  other  than  sodium  or  potassium  must  not  be  present, 
as  they  interfere  by  forming  insohible  antimonates. 

2.  PtCl4,  platinic  chloride,  as  well  as  H2C4H4O6,  tartaric 
acid,  fails  to  produce  a  precipitate  in  solutions  of  salts  of 
sodium. 

3.  Compounds  of  sodium  impart  to  the  flame  an  intense 
yellow  color. 

AMMONIUM,  NH4. 

The  radical  NH4  in  its  behavior  with  acid  radicals  corre- 
sponds to  potassium  and  sodium.  Another  analogy  between 
the  radical  ammonium  and  the  metals  is  the  existence  of  an 
ammonium  amalgam. 

NH±Cl,  ammonium  chloride,  may  be  employed  in  making  the 
tests. 

1.  The   ammonium    salts  (in   combination   with   volatile 


57 

acids)  are  characterized  by  their  complete  volatility  when 
heated  to  high  temperatures ;  ammonium  borate  and  ammo- 
nium phosphate,  however,  on  being  strongly  heated  leave  a 
residue  respectively  of  boric  acid  and  of  phosphoric  acid. 

2.  PtCl4,  platinic  chloride,  precipitates  in  concentrated  so- 
lutions yellow,  crystalline  (NH4Cl)2PtCl4,  ammonium  platinic 
chloride,  slightly  soluble  in  water,  insoluble  in  alcohol.     The 
test  is  best  made  in  a  watch-glass,  stirring  the  liquid  with  a 
glass  rod.     The  addition  of  a  little  alcohol  and,  if  the  am- 
monium salt  is  not  a  chloride,  a  drop  of  hydrochloric  acid 
hastens  the  formation  of  the  precipitate. 

3.  NaOH  or  KOH  added  to  a  solution  of  a  salt  of  am- 
monium liberates  ammoniacal  gas,  on  boiling  the  solution, 
which  may  be  detected  by  its  odor ;  by  its  producing  white 
clouds  of  ammonium  acetate  when  a  glass  rod  wet  with  acetic 
acid  is  held  above  the  liquid ;  by  its  action  upon  turmeric 
paper  moistened  with  water,  which  becomes  brown  when  held 
above  the  liquid  in  which  the  liberation  has  occurred ;  and 
by  its  action  upon   filter  paper  moistened  with  mercurous 
nitrate,  which  becomes  black  when  held  in  the  evolved  gas 
(due  to  the  formation  of  black  NH2Hg2NO3). 

4.  H2C4H4O6,  tartaric  acid,  or  NaHC4H4O6,  acid  sodium 
tartrate,  produces  in  concentrated  solutions  of  ammonium  salts 
white,  crystalline  NH4HC4H4O6,  acid  ammonium  tartrate. 

(For  conditions  favoring  precipitation    see  Potassium,  2, 
page  55.) 

LITHIUM,  Li. 
Atomic  weight,  7.O;  valence,  I. 

Silver-white  metal ;  specific  gravity,  0.59 ;  melting-point, 
180°  C. 

LiCl,  lithium  chloride,  may  be  employed  in  making  the  tests. 


58 

1.  NajCOg  precipitates,  in  cold  concentrated  solutions  of 
salts  of  lithium,  white  Li2CO3,  lithium  carbonate. 

2.  NaJHPC^  added  to  a  solution  of  a  salt  of  lithium  pro- 
duces a  white,  crystalline  precipitate  of  Li3PO4,  lithium  phos- 
phate. 

3.  Compounds  of  lithium  impart  to  the  flame  a  carmine- 
red  color. 


II.  PROPERTIES  OF  THE  ACIDS. 


FIRST  GROUP. 

ACIDS  which  are  precipitated  by  BaCl2,  barium  chloride, 
from  neutral  and  from  acid  solutions :  Sulphuric  Acid, 
Hydrofluosilicic  Acid. 

SULPHURIC  ACID,   H2SO4. 

(Sulphuric  acid  combines  with  bases  to  form  salts  called 
sulphates.) 

MgSOt,  magnesium  sulphate,  may  be  employed  in  making 
the  tests. 

1.  The  neutral  sulphates,  with  the  exception  of  barium, 
strontium,  calcium,  and  lead  sulphates,  are  easily  soluble  in 
water.     Basic  sulphates  of  the  heavy  metals  are  soluble  in 
hydrochloric  acid  or  in  nitric  acid.     Lead  sulphate  and  the 
sulphates  of  the  alkaline  earths  are  decomposed  and   con- 
verted into  carbonates  by  sodium  or  potassium  carbonate. 

2.  BaCl2,  barium  chloride,  precipitates,  from  solutions  con- 
taining sulphates  or  free  sulphuric  acid,  white,  pulverulent 
BaSO4,  insoluble  in  acids. 

3.  Pb(C2H3O2)2,  plumbic  acetate,  precipitates  white  PbSO4, 
plumbic  sulphate,  insoluble  in  dilute  acetic  acid,  somewhat 
soluble  in  boiling  concentrated  acids.     Plumbic  sulphate  is 
easily  soluble  in  (NH4)2C4H4O6,  ammonium  tartrate ;    from 
this  solution  potassium   chromate   precipitates   the   lead   as 
yellow  PbCrO4,  plumbic  chromate. 

4.  Sulphates,  fused  with   sodium   carbonate   on   charcoal, 

59 


60 

yield  a  residue  containing  !N"a2S,  sodium  sulphide.  On 
placing  a  portion  of  the  mass  on  a  clean  silver  coin  and 
adding  a  few  drops  of  water,  a  brownish  or  black  stain  of 
Ag2S  is  produced : 

C2  ==  NaJ3  -f  2CO2 ; 
-f  Ag2  -f  2H2O  =  Ag2S  -f  2NaOH  +  H2. 


HYDROFLUOSILICIC  ACID,  H.,SiF6. 

(Hydrofluosilicic  acid  combines  with  bases  to  form  salts 
called  silicofluorides.) 


iFfi,  sodium  silicofluoride,  may  be  employed  in  making 
the  tests. 

1  .  Most  of  the  silicofluorides  are  soluble  in  water  ;  when 
gently  heated  with  concentrated  sulphuric  acid,  they  evolve 
gaseous  SiF4,  silicon  fluoride,  and  HF,  hydrofluoric  acid  : 

K2SiF6  -f  H2S04  =  SiF4  +  2HF  +  K2SO4. 
If  a  piece  of  platinum  foil  containing  a  drop  of  water  be 
inverted  over  the  vessel  in  which  the  decomposition  is  effected, 
the  water  becomes  milky  in  appearance,  due  to  the  formation 
of  insoluble  H2SiO3,  silicic  acid  : 

3H2O  +  3SiF4  =  H2SiO3  -f  2H2SiF6. 

2.  BaCl2,    barium   chloride,   precipitates,    in  solutions   of 
hydrofluosilicic  acid  and  of  silicofluorides,  crystalline  BaSiF6, 
barium  silicofluoride,  insoluble  in  dilute  acids. 

3.  KNO3,  potassium  nitrate,  precipitates,  in  solutions  that 
are  not  too  dilute,  translucent,  gelatinous  K2SiF6,  potassium 
silicofluoride,  soluble  with   difficulty  in  water,  insoluble   in 
alcohol. 

4.  NH4OH    produces    NH4F,    ammonium    fluoride,   and 
H2SiO3,  silicic  acid,  both  of  which  are  precipitated  : 

6NH4OH  -f  H2SiF6  =  H2SiO3  +  6NH4F  4-  3H2O. 


61 


SECOND  GROUP. 

Acids  which  are  precipitated  by  BaCl2,  barium  chloride,  in 
neutral  solutions,  the  barium  salts  of  which  are  soluble  in 
hydrochloric  acid :  Sulphurous  Acid,  Hypo  sulphurous  Acid, 
Phosphoric  Acid,  Boric  Acid,  Hydrofluoric  Acid,  Carbonic 
Acid,  Silicic  Acid,  Chromic  Acid,  Arsenic  Acid,  Arsenious 
Acid. 

SULPHUROUS  ACID,   H2SO3. 

(Sulphurous  acid  combines  with  bases  to  form  salts  called 
sulphites.) 

Na2SOB,  sodium  sulphite,  may  be  employed  in  making  the  tests. 

1.  Of  the  neutral  sulphites  only  those  of  the  alkalies  are 
soluble  in  water ;  the  others  are  easily  soluble  in  acids,  with 
the  evolution  of  SO2,  sulphurous  anhydride  : 

BaSO3  +  2HC1  =  BaCl2  +  SO2  +  H2O. 

2.  Dilute  acids  decompose  sulphites,  with  the  evolution  of 
SO2,  sulphurous  anhydride,  which  may  be  recognized  by  its 
odor  (that  of  burning  sulphur).     The  presence  of  sulphurous 
anhydride  may  be  detected  in  gaseous  mixtures  by  its  be- 
havior with  KIO3,  potassium  iodate.     A  piece  of  filter  paper 
saturated  with  a  solution  of  potassium  iodate  and  starch  paste, 
brought  while  wet  in  contact  with  gaseous  mixtures  contain- 
ing sulphurous  anhydride,  becomes  blue  in  color,  owing  to 
the  reduction  of  HIO3,  iodic  acid,  to  iodine,  and  the  action 
of  the  latter  on  the  starch.      By  means  of  the  sulphurous 
anhydride,  in  the  presence  of  water,  the  iodic  acid  is  reduced 
to  HI,  hydriodic  acid  : 

3SO2  +  3H2O  +  HIO3  =  HI  +  3H2SO4. 
The  hydriodic  acid,  by  the  action  of  the  remaining  iodic 
acid,  is  reduced,  with  the  liberation  of  free  iodine : 
5HI-f  HI03  =  I6  +  3H20. 

6 


62 

(As  the  free  iodine  is  reconverted  by  an  excess  of  sulphurous 
anhydride  into  hydriodic  acid  : 

I2  -f  SO2  +  2H2O  =  2HI  -f-  H2SO4, 

an  excess  of  the  sulphurous  anhydride  causes  a  disappearance 
of  the  color.) 

3.  BaCl2  precipitates  white  BaSO3,  barium  sulphite,  soluble 
in  acids. 

4.  Pb(C2H3O2)2  precipitates  white  PbSO3,  plumbic  sulphite, 
soluble  in  nitric  acid. 

5.  AgNO3,    argentic   nitrate,    precipitates   white   Ag2SO3, 
argentic   sulphite,  soluble   in   nitric   acid.     On  boiling   the 
precipitate  with  w^ater,  it  is  decomposed  into  metallic  silver 
and  sulphuric  acid,  the  liquid  becoming  gray  in  color,  due 
to  the  separated  metallic  silver  : 

Ag2S03  +  H20  =  Ag2  -f-  H2S04. 

6.  ZnSO4,    zinc    sulphate    solution,    containing    a    little 
Na2NOFe(CN)5,  sodium  nitroprusside,  added  to  a  solution 
of  a   sulphite  which,  if  not   neutral,  has   been   neutralized 
with  acetic  acid,  produces  a  red  coloration ;  or  a  flocculent, 
purplish-red  precipitate,  if  the  solution  contain  a  considerable 
quantity  of  the  sulphite.     When  operating  with  dilute  solu- 
tions of  a  sulphite,  the  test  may  be  .made  more  delicate  by 
the  addition  of  a  few  drops  of  potassium  ferrocyanide  solu- 
tion.    (Distinction  from  hyposulphites.) 

7.  H2S  conducted  into  a  solution  of  sulphurous  acid  de- 
composes the  latter,  with  the  separation  of  sulphur  and  the 
probable  formation  of  H2S5O6,  pentathionic  acid  : 

5S02  +  5H2S  =  H2S506  -f  S5  +  4H2O. 

8.  Sulphites  ignited  with   sodium   carbonate  on  charcoal 
yield  a  yellowish  residue  containing  sodium  sulphide,  as  in 
the  case  of  sulphates.     A  portion  of  the  residue  placed  on  a 
clean  silver  coin  and  moistened  with  a  few  drops  of  water  pro- 
duces a  brown  or  black  stain  of  argentic  sulphide  on  the  coin. 


63 


HYPOSULPHUROUS     ACID,     H2S2O3    (THIOSULPHURIC 

ACID). 

(Hyposulphurous  or  thiosulphuric  acid  combines  with  bases 
to  form  salts  called  hyposulphites  or  thiosulphites.) 

Na2S2Os,  sodium  hyposulphite,  may  be  employed  in  making 
the  tests. 

1.  Most  of  the  hyposulphites  (thiosulphites)  are  soluble  in 
water. 

2.  HC1  or  H2SO4  added  to  a  solution  of  a  hyposulphite 
liberates  H2S2O3,  hyposulphurous  acid,  which  quickly  breaks 
up  into  sulphur,  sulphurous  anhydride,  and  water  : 

Na2S2O3  +  2HC1  =--  H2S2O3  +  2NaCl  ; 


Thus  hyposulphites,  on  the  addition  of  either  of  the  above 
acids,  are  decomposed  and  yield  sulphurous  anhydride,  which 
may  be  recognized  by  its  odor,  and  free  sulphur. 

3.  BaCl2,  barium  chloride,  produces  in  concentrated  solu- 
tions of  hyposulphites  a  white  precipitate  of  BaS2O3,  barium 
hyposulphite,  soluble  in  a  large  quantity  of  water.     It  is  also 
soluble  in  hydrochloric  acid,  with  the  evolution  of  sulphurous 
anhydride  and  the  separation  of  sulphur. 

4.  Pb(C2H3O2)2,  plumbic  acetate,  precipitates  white  PbS2O3, 
plumbic  hyposulphite,  soluble  in  nitric  acid. 

5.  AgNO3,  argentic   nitrate,  precipitates   white   Ag2S2O3, 
argentic  hyposulphite,  soluble  in  excess  of  sodium  hyposul- 
phite solution  : 

Ag2S203  +  Na2S203  =  2NaAgS203. 

The  precipitate  becomes  almost  immediately  yellow,  then 
brown,  and  finally  black,  due  to  the  formation  of  argentic 
sulphide  : 

Ag2S2O3  +  H2O  =  Ag2S  +  H2SO4. 


64 

6.  Fe2Cl6,  ferric  chloride,  immediately  colors  hyposulphite 
solutions  reddish  violet.     (Distinction  from  sulphites.) 

7.  Hyposulphites  ignited  with  sodium  carbonate  on  char- 
coal yield  a  residue  containing  sodium   sulphide,  as  in  the 
case  of  sulphates  and  of  sulphites.     A  portion  of  the  residue 
placed  on  a  clean  silver  coin  and  moistened  with  water  pro- 
duces a  brown  or  black  stain  of  argentic  sulphide. 

PHOSPHORIC    ACID,    H3PO4. 

(Phosphoric  acid  combines  with  bases  to  form  salts  called 
phosphates.) 

Na2HPO^  sodium  hydrogen  phosphate,  may  be  employed  in 
making  the  tests. 

1.  The  phosphates  of  the  alkalies  are  soluble  in  water,  the 
others  are  soluble  in  acids. 

2.  BaCl2,  barium  chloride,  precipitates  in  solutions  of  the 
neutral  phosphates  white  BaHPO4  or  Ba3(PO4)2,  soluble  in 
hydrochloric  acid  or  in  nitric  acid. 

3.  Pb(C2H3O2)2,     plumbic     acetate,     precipitates     white 
Pb3(PO4)2,  soluble  in  nitric  acid. 

4.  AgNO3,  argentic  nitrate,  produces  in  solutions  of  the 
phosphates  a  light-yellow  precipitate  of  Ag3(PO4),  soluble  in 
nitric  acid  and  in  ammonium  hydroxide. 

5.  NH4C1,  ammonium  chloride,  NH4OH,  ammonium  hy- 
droxide, and  MgSO4,  magnesium  sulphate,(l)  added  in  turn  to 
a  solution  of  a  phosphate,  produce  a  white,  crystalline  pre- 
cipitate of  MgNH4PO4,  ammonium  magnesium  phosphate  : 

Na2HPO4  +  NH4OH  +  MgSO4  =  MgNH4PO4  + 


(The  ammonium  chloride  is  added  to  prevent  the  precipitation 
of  the  magnesium  as  magnesium  hydroxide  by  the  ammo- 

1  The  three  reagents  composing  the  so-called  "magnesia  mixture." 


65 

nium  hydroxide.)  The  precipitate  is  sparingly  soluble  in 
pure  water,  and  very  slightly  soluble  in  water  containing 
ammonium  hydroxide.  In  precipitating  very  dilute  solu- 
tions the  precipitate  forms  more  rapidly  when  the  inner  sides 
of  the  vessel  are  gently  rubbed  with  a  glass  rod. 

6.  NH4HMoO4,  ammonium  molybdate,  added  in  excess, 
with  a  considerable  quantity  of  nitric  acid,  to  a  solution  of 
phosphoric  acid  or  a  phosphate,  produces  a  yellow  precipitate, 
probably  of  (NH4)3PO4(MoO3)10,  ammonium  phosphomolyb- 
date : 
10NH4HMoO4  +  H3PO4  +  7HNO3  ==  (NH4)3PO4(MoO3)10  + 

7NH4N03  +  10H20. 

The  precipitate  is  insoluble  in  dilute  nitric  acid,  but  easily 
soluble  in  ammonium  hydroxide ;  it  is  reprecipitated  from 
the  ammoniacal  solution  by  the  addition  of  excess  of  nitric 
acid.  The  precipitate  is  also  soluble  in  excess  of  a  phosphate, 
and  thus  is  explained  the  non-appearance  of  a  precipitate 
when  only  a  little  ammonium  molybdate  is  added  to  a  solu- 
tion containing  much  phosphoric  acid.  In  dilute  solutions 
the  precipitate  forms  slowly.  The  precipitation  is  hastened 
by  warming  the  solution  to  a  temperature  of  40°  C.  A 
higher  temperature  should  be  avoided. 

(Pyrophosphates  yield  with  argentic  nitrate  white  precip- 
itates of  Ag4P2O7,  argentic  pyrophosphate.  Metaphosphates 
likewise  yield  white  precipitates  of  AgPO3.  Only  the  meta- 
phosphates  coagulate  albumen.) 

BORIC  ACID,  H3B03. 

(Boric  acid  combines  with  bases  to  form  salts  called 
borates.) 

JVa2I>407,  sodium  biborate  (borax),  may  be  employed  in 
making  the  tests. 


66 

1.  Of  the  borates  those  of  the  alkalies  are  easily  soluble 
in  water. 

2.  BaCl2,  barium  chloride,  produces  in  concentrated  solu- 
tions of  borates  white  Ba(BO2)2,  barium  metaborate,  easily 
soluble  in  excess  of  barium  chloride  and  in  ammonium  chlo- 
ride : 

2BaCl2  +  H2O  =  2Ba(BO2)2  +  2NaCl  +  2HC1. 


3.  Pb(C2H3O2)2,   plumbic  acetate,  precipitates  in  concen- 
trated solutions  white  Pb(BO2)2,  4japmm.  metaborate,  soluble 
in  excess  of  the  reagent. 

4.  AgNO3,    argentic   nitrate,  precipitates   in  concentrated 
solutions  of  neutral  borates  white  AgBO2,  argentic  metaborate, 
which  is  occasionally  tinged  with  yellow,  due  to  the  presence 
of  argentic  oxide.     In  solutions  of  acid  borates  the  precipitate 
is  Ag6B8O15.    Both  precipitates  are  easily  soluble  in  nitric  acid. 

5.  Boric  acid,  in  the  powdered  condition,  placed  in  a  porce- 
lain dish  and  covered  with  alcohol  gives  a  greenish  flame  on 
igniting  the  alcohol.      Borates,  in  the   powdered  condition, 
impart  the  same  greenish  color  to  the  flame,  but  must  be 
moistened  with  a  few  drops  of  concentrated  sulphuric  acid 
before  the  addition  of  the  alcohol.     The  greenish  color  im- 
parted to  the  flame  is  due  to  (C2H5)3BO3,  the  ethyl  ester  of 
boric  acid,  formed  in  the  reaction.     Boric  acid  (without  the 
addition  of  alcohol)  when  strongly  heated  on  platinum  wire 
imparts  a  greenish  color  to  the  flame.     (Compounds  of  barium 
and  of  copper  and  compounds  containing  chlorine  interfere 
with  the  test.) 

6.  Turmeric  paper  dipped  in  an  aqueous  solution  of  boric 
acid,  or  in  a  solution  of  a  borate  acidified  with  hydrochloric 
acid,  and  warmed  until  dry,  becomes  reddish  brown  in  color. 
On  bringing  dilute  sodium  or  potassium  hydroxide  solution 
in  contact  with  the  reddish-brown  paper,  the  color  becomes 
blue  and  then  greenish  black. 


67 


HYDROFLUORIC  ACID,  HF. 

(Hydrofluoric  acid  combines  with  bases  to  form  salts  called 
fluorides.) 

KFj  potassium  fluoride,  or  NaF,  sodium  fluoride,  may  be 
employed  in  making  the  tests. 

1 .  Of  the  fluorides  those  of  the  alkalies  are  easily  soluble 
in  water,  the  others  are  soluble  only  with  great  difficulty. 

2.  BaCl2   precipitates    from   solutions   of    fluorides   white 
BaF2,  soluble  in  hydrochloric  acid ;  Pb(C2H3O2)2  precipitates 
white  PbF2,  easily  soluble  in  nitric  acid ;  and  AgNO3  pre- 
cipitates white  AgF,  also  easily  soluble  in  water. 

3.  CaCl2,  calcium   chloride,  precipitates  white,   gelatinous 
CaF2,  calcium  fluoride,  almost  insoluble  in  water,  soluble  with 
difficulty  in  mineral  acids. 

4.  Hydrofluoric  acid  has  the  property  of  etching  glass, 
forming  with  the  silicic  oxide  of  the  glass  volatile  SiF4,  silicon 

fluoride : 

,  -      SiO2  +  4HF  =  SiF4  +  2H2O. 

The  test  is  performed  in  a  platinum  crucible  covered  with  a 
watch-glass.  The  convex  side  of  the  watch-glass  is  covered 
with  melted  wax,  and,  after  the  wax  has  cooled,  a  design 
or  figure  is,  by  means  of  a  sharpened  piece  of  wood  or  the 
point  of  a  knife-blade,  graven  of  sufficient  depth  in  the  wax 
to  expose  an  uncoated  surface  of  glass.  The  pulverized 
fluoride  is  placed  in  the  crucible,  moistened  with  concen- 
trated sulphuric  acid,  quickly  covered  with  the  watch-glass 
(waxed  side  down),  and  the  whole  placed  on  a  moderately 
warm  iron  plate  or  porcelain  dish.(l)  After  some  time  the 
watch-glass  is  taken  from  the  crucible,  and  when  the  wrax 

1  The  watch-glass  should  be  filled  with  cold  water,  to  prevent  the  melt- 
ing of  the  wax. 


68 

is   removed   the  graven  design   will   appear  etched   in   the 
glass. 

5.  In  decomposing  fluorides  containing  considerable  silicic 
acid  with  concentrated  sulphuric  acid,  gaseous  SiF4  is  evolved, 
which,  when  conducted  through  a  glass  tube  moistened  with 
Avater,  undergoes  decomposition,  rendering  the  water  turbid, 
with  the  deposition  of  silicic  acid : 

3SiF4  +  3H20  =  H2Si03  +  2H2SiF6. 

The  result  of  the  reaction  is  especially  observable  on  drying 
the  tube. 

CARBONIC  ACID,  H2CO3- 

(Carbonic  acid  combines  with  bases  to  form  salts  called  car- 
bonates.) 

Na2COB,  sodium  carbonate,  may  be  employed  in  making  the 


1.  The  carbonates  of  the  alkalies  are  soluble  in  water,  the 
other  carbonates  are  insoluble  in  water.     Many  of  the  latter 
are,  however,  soluble  in  water   containing   carbon   dioxide, 
forming  acid  carbonates  : 

CaCO3  +  C02  +  H,0  =  Ca(HC03)2. 

Carbonates  in  general  readily  dissolve  in  dilute  acids,  with 
effervescence  (due  to  the  liberation  of  carbon  dioxide).  The 
metal  of  the  carbonate  forms  a  salt  with  the  acid  used  as  a 
solvent : 

BaC03  +  2HC1  =  BaCl2  -f-  CO2  +  H2O. 

2.  HC1  or  any  dilute  acid  (except  hydrocyanic  acid),  added 
to  a  carbonate  either  in  solution  or  in  the  solid  condition, (l) 
produces  effervescence,  due  to  the  evolution  of  carbon  dioxide. 

1  The  minerals  magnesite  (MgCO3),  dolomite  (CaCO3,MgCO3),  and 
siderite  (FeCO3)  produce  effervescence  with  a  dilute  acid  only  after  being 
warmed. 


69 

The  latter  may  be  detected  by  inclining  the  test-tube  in  which 
the  effervescence  has  taken  place  so  as  to  pour  only  the  gas- 
eous CO2  into  another  test-tube  containing  clear  calcium  hy- 
droxide solution.  The  CO2,  being  specifically  heavier  than 
air,  displaces  the  air  in  the  tube  containing  calcium  hy- 
droxide, and,  on  closing  the  latter  tube  with  the  thumb  and 
agitating  the  liquid,  a  turbidity  is  produced,  due  to  the  for- 
mation of  CaCO3,  calcium  carbonate : 

C02  +  Ca(OH)2  =  CaC03  +  H2O. 

3.  BaCl2,   barium    chloride,    precipitates    white    BaCO3, 
barium  carbonate ;  Pb(C2H3O2)2,  plumbic  acetate,  precipitates 
white  PbCO3 ;  both  are  soluble  with  effervescence  in  dilute 
acids. 

4.  AgNO3,  argentic    nitrate,  precipitates   white   Ag2CO3, 
argentic  carbonate,  which  in  a  little  time  becomes  yellowish, 
and  on  being  boiled  with    an  excess  of  sodium  carbonate 
changes  to  brownish-gray  Ag2O,  argentic  oxide.     The  argen- 
tic oxide  is  soluble  in  ammonium  hydroxide  and  in  ammo- 
nium carbonate. 

SILICIC  ACID,   H2SiO3. 

(Silicic  acid  combines  with  bases  to  form  salts  called  sili- 
cates.) 

Na2Si03,  sodium  silicate,  may  be  employed  in  making  the  tests. 

1.  Of  the  silicates  only  those  of  the  alkalies  are  solu- 
ble in  water,  the  others  are  partially  soluble  in  concentrated 
acids. 

The  addition  of  an  acid  (as  hydrochloric  acid)  to  a  solution 
of  a  silicate  of  an  alkali  causes  the  separation  of  silicic  acid, 
which,  if  the  solution  is  of  sufficient  concentration,  appears  as 
a  gelatinous  precipitate ;  ammonium  chloride  also  separates 
silicic  acid  from  solutions  of  silicates  of  the  alkalies : 


70 

Na2Si03  +  2HC1  =  H2SiO3  +  2NaCl ; 
Na2Si03  -f  2JSTH4C1  +  2H2O  =  H2SiO3  +  2NaCl  +  2NH4OH. 
The  silicic  acid  separated  in  this  manner  is  somewhat  soluble 
in  dilute  acids.  On  evaporating  the  solution  containing  silicic 
acid — i.e.,  the  solution  with  the  precipitate  in  suspension — to 
the  dryness  of  dust  on  a  water-bath,  the  silicic  acid  loses 
water  and  amorphous  silicic  acids  are  produced, — i.e.,  poly- 
silicic  acids,  H2Si4O9,  for  example,  which  are  entirely  insolu- 
ble in  water : 

4H2Si03  =  H2Si409+3H20. 

On  extracting  the  residue  with  water  containing  a  little  hy- 
drochloric acid,  the  metal  which  had  originally  been  in  com- 
bination with  the  silicic  acid  is  dissolved  as  a  chloride,  while 
the  silicic  acid  remains  undissolved.  Evaporation  over  a  free 
flame  is  not  advised,  as  thereby  (because  of  the  stability  of 
silicic  acid  when  heated)  a  part  of  the  salt  might  be  recon- 
verted into  silicates,  as,  for  example : 

H2Si4O9  +  2NaCl  =  Na^A  +  2HC1. 
For  the  methods  employed  in  dissolving  and  disintegrating 
silicates  insoluble  in  water,  see  Silicates,  page  112. 

2.  BaCl2,   barium  chloride,   precipitates   in    solutions    of 
silicates   of   the    alkalies    white    BaSiO3,   barium    silicate; 
Pb(C2H3O2)2,    plumbic   acetate,   precipitates   white    PbSiO3, 
plumbic  silicate ;  AgNO3,  argentic  nitrate,  precipitates  yellow- 
ish Ag2SiO3,  argentic  silicate ;  all  soluble  in  acids,  the  argen- 
tic silicate  being  also  soluble  in  ammonium  hydroxide. 

3.  NH4HMoO4,  ammonium  molybdate,  together  with  an 
excess  of  nitric  acid,  added  to  a  solution  of  a  silicate  pro- 
duces a  yellowish  coloration,  and,  in  the  presence  of  con- 
siderable  ammonium   chloride,   a   lemon-yellow  precipitate. 
Warming  facilitates  the  reaction. 

4.  On  fusing  a  silicate  with  microcosmic  salt  in  the  loop  of 
a  platinum  wire,  the  sodium  metaphosphate  which  is  produced 


71 

dissolves  the  base,  while  the  silicic  acid  remains  undissolved 
and  swims  in  small  opaque  particles  in  the  otherwise  trans- 
parent bead  while  the  latter  is  in  a  state  of  fusion  ("  skeleton 
of  silica") ;  for  example  : 

CaSi03  +  NaP03  =  CaNaPO4  +  SiO2. 

Uncombined  silicic  acid  produces  the  same  result.  The  reac- 
tion is  made  more  evident  by  coloring  the  bead  with  a  com- 
pound of  copper  or  of  iron. 

ARSENIOUS  ACID,  H3AsO3.    (See  page  21.) 

ARSENIC  ACID,  H3AsO4.    (See  page  26.) 

CHROMIC    ACID,  H2CrO4. 

(Chromic  acid  combines  with  bases  to  form  salts  called 
chromates.) 

K2CrO^  potassium  chromatej  may  be  employed  in  making 
the  tests. 

1.  Most  of  the  chromates  are  insoluble  in  water.     The 
chromates  of  the  alkalies  (the  neutral  salts)  are  easily  solu- 
ble ;    the  bichromates  (the  so-called  acid  salts)  are  soluble, 
with  the  production  of  a  reddish-yellow  color. 

2.  BaCl2,  barium  chloride,  precipitates  from  solutions  of 
chromates   yellow   BaCrO4,   barium  chromate,  soluble  with 
great  difficulty  in  water,  soluble  in  hydrochloric  and  in  nitric 
acids. 

3.  Pb(C2H3O2)2,  plumbic  acetate,  precipitates  yellow,  crys- 
talline PbCrO4,  plumbic  chromate  (chrome-yellow),  insoluble 
in  water  and   in  acetic  acid,  soluble  in  nitric  acid  and  in 
sodium    hydroxide,    in    the   latter   with   the   formation    of 
Na2CrO4,  sodium  chromate,  and  Pb(ONa)2,  sodium  plum- 
bite  ;  acetic  acid  reprecipitates  lead  chromate  from  the  sodium 
hydroxide  solution. 


72 

4.  AgNO3,  argentic  nitrate,   precipitates   in   solutions  of 
chromates  purplish-red  Ag2CrO4,  argentic  chromate,  and  in 
solutions  of  bichromates  purplish-red  Ag2O2O7,  argentic  bi- 
chromate, both   soluble  in  nitric   acid   and   in   ammonium 
hydroxide. 

5.  H2S,  hydrogen  sulphide,  conducted  into  a  solution  of  a 
chromate  containing   considerable  free  hydrochloric  acid  or 
sulphuric  acid,  reduces  the  chromate,  with  the  formation  of 
a  soluble  chromic   salt  and  the  separation  of  sulphur,   the 
solution  at  the  same  time  becoming  green  in  color : 
2K2CrO4  +  3H2S  +  10HC1  =  O2C16  -f  S3  +  4KC1  +  8H2O. 
In   case    the    acid   is   present   in   small    quantity,   greenish 
Cr2(OH)6,  chromic  hydroxide,  or  (especially  on  warming  the 
solution)  brown  chromium  chromate  is  precipitated  : 

2K2CiO4  +3H2S  +  4HC1  =  O2(OH)6  +  S3  -f  4KC1  + 

2H20; 
3K2CrO4  +  3H2S  +  6HC1  =  (CrO)2CrO4  +  S3  +  6KC1 

+  6H20. 

The  action  of  ammonium  sulphide  in   neutral  or   alkaline 
solutions  of  chromates  is  similar  to  that  of  hydrogen  sulphide. 

6.  On  adding  C2H5OH,  alcohol,  to  a  solution  of  a  chromate 
or  bichromate  containing  free  hydrochloric  or  sulphuric  acid, 
and  warming  the  liquid,  the  chromate  is  reduced  to  a  chromic 
salt,  while  the  alcohol   is  oxidized  to  C2H4O,  aldehyde;  in 
consequence,  the  liquid  becomes  green  in  color  and  the  odor 
of  aldehyde  becomes  evident : 

K2Cr207  -j-  4H2S04  -f  3C2H5OH  =  Cr2(SO4)3  +  3C2H4O  + 
K2SO4  +  7H2O. 

7.  Chromates  fused  in  a  bead  of  borax  or  of  microcosmic 
salt  impart  a  yellowish-green  color  to  the  bead  while  hot, 
which  becomes  emerald-green  on  cooling. 


73 


THIRD  GROUP. 

Acids  which  are  not  precipitated  by  BaCl2,  barium  chloride, 
but  are  precipitated  by  AgNO3,  argentic  nitrate  :  Hydrochloric 
Acid,  Hydrobromic  Acid,  Hydriodic  Acid,  Hydrocyanic  Acid, 
Hydroferro cyanic  Acid,  Hydroferricyanic  Acid,  Sulphydric 
Acid  (Hydrogen  Sulphide),  Nitrous  Acid,  Hypochlorous  Acid. 

HYDROCHLORIC  ACID,  HC1. 

(Hydrochloric  acid  combines  with  bases  to  form  salts  called 
chlorides.) 

NaCl,  sodium  chloride,  may  be  employed  in  making  the  tests. 

1.  The  chlorides  are  soluble  in  water,  with  the  exception 
of  argentic  chloride,  mercurous  chloride,  and  plumbic  chlo- 
ride;   the  latter,  however,  being   sparingly  soluble  in  cold 
water.     (For  dissolving  insoluble  chlorides,  see    Dissolving 
Oxides  and  Salts,  page  104.)        t 

2.  AgNO3,  argentic  nitrate,  precipitates  white,  curdy  AgCl, 
argentic  chloride,  insoluble  in  dilute  nitric  acid,  easily  soluble 
in  ammonium  hydroxide.     From  its  solution  in  ammonium 
hydroxide  the  argentic  chloride   is   reprecipitated   by  nitric 
acid.     The  precipitate  is  also  soluble  in   KCN,  potassium 
cyanide,  and  in  Na2S2O3,  sodium  hyposulphite.     When  ex- 
posed to  sunlight  the  precipitate  changes  in  color  to  violet  and 
then  to  black. 

3.  Pb(C2H3O2)2,  plumbic    acetate,  precipitates,  in   hydro- 
chloric acid  and  in  solutions  of  chlorides,  white,  sometimes 
crystalline  PbCl2,  plumbic  chloride,  sparingly  soluble  in  cold 
water,  easily  soluble  in  hot  water,  from  which,  when  in  con- 
centrated   solution,  it  crystallizes,  on  cooling,  in  glistening 
rhombic  needles.     Precipitation  does  not  occur  in  very  dilute 
solutions  of  chlorides. 


74 

4.  On  placing  a  dry  mixture  of  a  chloride  and  potassium 
bichromate  in  a  small  retort  or  tubulated  fractionating  flask, 
adding  concentrated  sulphuric  acid,  and  carefully  distilling 
the  contents  of  the  retort,  CrO2Cl2,  chlorochromic  anhydride, 
as  a  brownish-red  gas,(1)  is  produced,  which,  when  conducted 
into  a  receiving  flask,  condenses  into  a  brownish-red  liquid : 
4KC1  +  K2Cr207  +  6H2SO4  =  2CrO2Cl2  +  6KHSO4  +  3H2O. 
Sodium  hydroxide  added  to  the  brownish-red  distillate  pro- 
duces a  yellowish  solution  of  N^CrO^,  sodium  chromate (2> 
(together  with  sodium  chloride) : 

CrOaCLj  +  4NaOH  ==  NajCrO*  +  2NaCl  +  2H2O. 
If  the  yellowish  solution  is  acidified  with  acetic  acid  and 
plumbic  acetate  added,  the  production  of  a  yellow  precipitate 
of  plumbic  chromate  gives  indirect  but  conclusive  evidence  of 
chlorine. 

HYDROBROMIC  ACID,   HBr. 

(Hydrobromic  acid  combines  with  bases  to  form  salts  called 
bromides.) 

KBr,  potassium  bromide,  may  be  employed  in  making  the 


1.  The  bromides  in  general  are  soluble  in  water.     Argentic 
bromide  and  mercurous  bromide  are  insoluble ;  plumbic  bro- 
mide is  sparingly  soluble  in  water. 

2.  AgNO3,  argentic   nitrate,  precipitates  yellowish-white, 
curdy  AgBr,  argentic  bromide,  insoluble  in  dilute  nitric  acid, 
sparingly  soluble  in  dilute  and  more  easily  soluble  in  concen- 
trated ammonium  hydroxide.    The  precipitate  is  easily  soluble 
in  potassium  cyanide  and  in  sodium  hyposulphite. 

3.  Pb(C2H3O2)2,   plumbic   acetate,  precipitates   in    hydro- 

1  Distinction  from  iodides,  which  furnish  violet-colored  vapors  of  free 
iodine. 

2  Distinction  from  bromides,  which  do  not  impart  a  color  to  the  liquid. 


75 

bromic  acid  and  in  solutions  of  bromides  white,  crystalline 
PbBr2,  plumbic  bromide,  sparingly  soluble  in  cold  water, 
more  easily  soluble  in  hot  water. 

4.  Dry  bromides,  on  being  distilled  in  a  retort  with  potas- 
sium bichromate  and  concentrated  sulphuric  acid  (see  under 
Chlorides,  4,  page  74),  yield  brown  vapors  of  bromine,  which 
condense  in  the  receiver  as  a  brown  distillate  of  bromine,  free 
from  chromium  : 

6KBr  +  K2Cr2O7  +  7H2SO4  =  Cr2(SO4)3  +  4K2SO4  -f 

7H20  +  Br6. 

Sodium  hydroxide  added  to  the  distillate  decolorizes  it,  form- 
ing sodium  bromide  and  NaBrO,  sodium  hypobromite  : 
Br2  +  2NaOH  =  NaBr  -f  NaBrO  -f  H2O. 

5.  Chlorine-water  added  in  small  quantity  to  a  solution  of 
a  bromide  liberates  bromine,  which  remains  dissolved  in  the 
water.     On  adding  a  small  quantity  of    chloroform  or  of 
carbon  disulphide  (both  of  which  are  insoluble  in  water  and 
sink  to  the  bottom  of  the  test-tube),  closing  the  mouth  of  the 
tube  with  the  thumb,  and  thoroughly  shaking  it,  the  chloro- 
form or  carbon  disulphide  extracts  the  bromine  and  collects 
at  the  bottom  of  the  tube  as  a  yellowish  or  brownish  liquid. 
The  depth  of  coloration  depends  upon  the  quantity  of  bromine 
present, 

If  an  excess  of  chlorine-  water  is  used,  decolorization  of  the 
liquid  occurs,  due  to  the  formation  of  HBrO3,  bromic  acid  : 


BrCl5  +  3H2O  =  HBrO3  -f  5HC1. 


HYDRIODIC  ACID,  HI. 

(Hydriodic  acid  combines  with  bases  to  form  salts  called 
iodides.) 

y  potassium  iodide,  may  be  employed  in  making  the  tests. 


76 

1.  Most  of  the  iodides  are  soluble  in  water;  tl^e  others  are 
soluble   in   acids,   with   the    exception   of   argentic    iodide. 
Plumbic  iodide  is  sparingly  soluble  in  cold  water. 

2.  AgNO3,  argentic  nitrate,  precipitates  yellowish,  amor- 
phous Agl,  argentic  iodide,  insoluble  in  nitric  acid  and  in 
ammonium  hydroxide,  soluble  in  potassium  cyanide  and  in 
sodium  hyposulphite. 

3.  Pb(C2H3O2)2,  plumbic  acetate,  precipitates  in  solutions 
of  hydriodic  acid  and  of  iodides  yellow,  crystalline   PbI2, 
plumbic  iodide,  soluble  in  hot  water,  from  which,  on  cooling, 
it  separates  in  glistening  yellow,  six-sided  plates. 

4.  Dry  iodides,  distilled  in  a  retort  with  potassium  bichro- 
mate and  concentrated  sulphuric  acid  (see  under  Chlorides,  4, 
page  74),  yield  violet  vapors  of  iodine  :(1) 

6KI  +  K2Cr207-f  7H2S04  =  Cr2(SO4)3  +  4K2SO4+  7H2O  + 16. 
The  iodine  contained  in  the  distillate  is  soluble  in  sodium 
hydroxide,  forming  Nal,  sodium  iodide,  and  NaIO3,  sodium 
iodate,  the  distillate  at  the  same  time  becoming  colorless : 
I6  +  6NaOH  =  5NaI  +  NaIOs  +  3H2O. 

5.  Chlorine-water  added  in  small  quantity  to  a  solution 
of  an  iodide  liberates  iodine,  which   imparts  a  yellowish  or 
brownish-yellow  color  to  the  solution.     On  adding  a  small 
quantity  of  chloroform  or  of  carbon  disulphide  to  the  liquid, 
closing  the  tube  with  the  thumb,  and  thoroughly  shaking  it, 
the  chloroform  or  carbon  disulphide  will  settle  at  the  bottom 
of  the  tube,  and  be  found  to  possess  a  blue  color,  due  to  the 
free  iodine  extracted  from  the  aqueous  solution. 

If,  instead  of  chloroform  or  carbon  disulphide,  a  drop  of 
dilute  starch  paste  is  added,  the  solution  becomes  blue,  due  to 
the  action  of  the  free  iodine  upon  the  starch.  The  test  is 
exceedingly  delicate,  and  when  considerable  iodine  is  present 

1  Distinction  from  chlorine  and  bromine. 


77 

the  liquid  becomes  black  upon  the  addition  of  the  starch  ; 
therefore  strong  solutions  of  iodides  should  be  diluted  before 
making  this  test. 

The  addition  of  an  excess  of  chlorine-water  causes  the 
oxidation  of  the  iodine  to  iodic  acid,  with  a  consequent 
decolorization  of  the  liquid  : 


IC15  +  3H20  =  HI03  +  5HC1. 


HYDROCYANIC  ACID,   HCN. 

(Hydrocyanic  acid  combines  with  bases  to  form  salts  called 
cyanides.) 

KCN,potassium  cyanide,  may  be  employed  in  making  the  tests. 

1.  Of  the  cyanides  those  of  the  alkalies  and  of  the  alkaline 
earths  are  soluble  in  water  (also  mercuric  cyanide)  ;  the  cya- 
nides of  the  heavy  metals  are  insoluble  in  water,  although 
many  of   them  are  soluble  in  potassium  cyanide,  with  the 
formation  of  double  salts  ;  for  example  : 

AgCN  +  KCN  ==  AgCN  KCN. 

By  the  addition  of  an  acid  to  these  solutions,  the  cyanide  of 
the  heavy  metal  is  usually  but  not  invariably  reprecipitated, 
with  the  evolution  of  hydrocyanic  acid  : 

AgCN  KCN  +  HNO3  =  AgCN  +  HCN  -f-KNO3. 
For  methods  of  dissolving  and  fusing  cyanides,  see  4,  page 
111. 

2.  AgNO3,  argentic   nitrate,  precipitates  in   solutions  of 
hydrocyanic  acid  and  of  cyanides  white,  curdy  AgCN,  in- 
soluble in  nitric  acid,  easily  soluble  in  ammonium  hydroxide. 
From  this  solution  it  is  reprecipitated  by  nitric  acid  : 

AgCN  +  NH3  =  NH3AgCN  ; 
NH3AgCN  +  HNO3  =  AgCN  +  NH4NO3. 
Argentic  cyanide  is  soluble  in  potassium  cyanide  ;  therefore 


78 

a  precipitate  appears  only  after  an  excess  of  argentic  nitrate 
has  been  added.  It  is  also  soluble  in  sodium  hyposulphite. 
On  igniting  argentic  cyanide  it  breaks  up  into  metallic  silver 
and  cyanogen  gas  (together  with  some  argentic  paracyanide)  : 

' 


3.  Pb(C2H3O2)2,  plumbic  acetate,  produces  in  solutions  of 
cyanides  a  white  precipitate  of    Pb(CN)2,  plumbic  cyanide, 
soluble  in  nitric  acid. 

4.  If  NaOH,  sodium  hydroxide,  FeSO4,  ferrous  sulphate, 
and  Fe2Cl6,  ferric  chloride,  are  added  in  small  quantities  to 
a  solution  of  hydrocyanic  acid  or  to  a  cyanide,  the  mixture 
warmed,  and  finally  acidulated  with  hydrochloric  acid,  a  blue 
precipitate  of  Fe4(Fe(CN)6)3,   ferric    ferrocyanide   (Prussian 
blue),  is  formed  ;  while  the  ferrous  hydroxide  first  produced 
is  dissolved   by  the   acid.     The  ferrous   sulphate  with   the 
sodium  hydroxide  produces  Fe(OH)2,  ferrous  hydroxide  : 

FeSO4  +  2NaOH  =  Fe(OH)2  +  Na2SO4, 
which,  on  being  warmed  with  the  cyanide  solution,  yields  a 
ferrocyanide  ;  for  example,  with  potassium  cyanide  it  yields 
K4Fe(CN)6,  potassium  ferrocyanide  : 

Fe(OH)2  +  6KCN  =  K4Fe(CN)6  +  2KOH, 
which  combines  with  the  iron  of  the  ferric  chloride  to  form 
blue  ferric  ferrocyanide  (Prussian  blue). 

5.  To  detect  hydrocyanic  acid  which  is  being  evolved  from 
a  liquid,  a  drop  of  yellow  ammonium  sulphide  and  of  ammo- 
nium hydroxide  is  placed  on  the  concave  side  of  a  watch- 
glass,  the  watch-glass  inverted  and  placed  as  a  cover  over  the 
vessel  in  which  the  hydrocyanic  acid  is  being  evolved,  so  that 
the  vapors  of  the  acid  coming  in  contact  with  the  ammoniacal 
liquid  can  be  absorbed.     After  some  time  the  watch-glass  is 
removed,   placed   on   a  water-bath,   and   warmed,    whereby 
NH4CNS,  ammonium  sulphocyanide,  is  produced  : 

HCN  +  (NH4\S2  +NH4OH  =  NH4CNS  +  (NH4)2S  +  H2O, 


79 

which  remains  as  a  dry  residue  on  the  complete  evaporation 
of  the  liquid.  This  residue  is  dissolved  in  a  little  water ;  a 
few  drops  of  hydrochloric  acid  (to  decompose  any  (NHJ2S 
remaining)  and  a  drop  of  ferric  chloride  are  added,  whereby 
a  claret-red  coloration  is  produced,  due  to  the  formation  of 
Fe2(CNS)6,  ferric  sulphocyanide. 

6.  When  heated  in  a  reduction- tube  the  cyanides  of  the 
heavy  metals  are  decomposed ;  the  cyanides  of  the  noble 
metals  break  up  into  metal  and  cyanogen  gas ;  other  cyanides 
break  up  into  metal,  carbon,  and  nitrogen.  Argentic  and 
mercuric  cyanides,  in  which  the  cyanogen  cannot  be  detected 
by  the  ordinary  reagents,  can  be  recognized  in  this  manner. 
Mercuric  cyanide  in  aqueous  solutions,  when  treated  with 
hydrogen  sulphide,  decomposes  and  forms  mercuric  sulphide 
and  hydrocyanic  acid.  HCN  and  CN  are  virulent  poisons. 

HYDROFERROCYANIC  ACID,   H4Fe(CN)6. 

(Hydroferrocyanic  acid  combines  with  bases  to  form  salts 
called  ferrocyanides.) 

K±Fe(CN)v  potassium  ferrocyanide,  may  be  employed  in 
making  the  tests. 

1.  The  ferrocyanides,  with  the  exception  of  those  of  the 
alkalies  and  of  the  alkaline  earths,  are  mostly  insoluble  in 
water.     Regarding  their  solution  and  fusion,  see  page  112. 

2.  AgNO3,  argentic  nitrate,  precipitates  white  Ag4Fe(CN)6, 
argentic  ferrocyanide,  insoluble  in  nitric  acid  and  in  ammo- 
nium hydroxide,  soluble  in  potassium  cyanide. 

3.  Pb(C2H3O2)2,   plumbic   acetate,    in   solutions  of  ferro- 
cyanides precipitates  white  Pb2Fe(CN)6,  plumbic  ferrocyanide, 
insoluble  in  dilute  nitric  acid. 

4.  Ferrous  salts  (FeSO4,  ferrous  sulphate)  produce  in  solu- 
tions of  ferrocyanides  (when  the  ferrocyanide  is  in  excess)  a 


80 

white  precipitate,  which,  on  exposure  to  the  air,  rapidly 
changes  to  bluish-white  K2Fe(Fe(CN)6),  potassium  ferrous 
ferrocyanide  (Everett's  salt).  When  the  ferrous  salt  is  in 
excess,  Fe2Fe(CN)6,  ferrous  ferrocyanide,  is  produced. 

5.  Ferric  salts  (Fe2Cl6,  ferric  chloride)  precipitate  dark-blue 
Fe4(Fe(CN)6)3,  ferric  ferrocyanide  (Prussian  blue),  insoluble 
in  acids. 

6.  CuSO4,    cupric    sulphate,    precipitates    brownish-red 
Cu2Fe(CN)6,  cupric  ferrocyanide. 


HYDROFERRICYANIC  ACID,  H3Fe(CN)6. 

(Hydroferricyanic  acid  combines  with  bases  to  form  salts 
called  ferricyanides.) 

K3Fe(CN)6,  potassium  ferricyanide,  may  be  employed  in 
making  the  tests. 

1.  Of  the  ferricyanides  those  of  the  alkalies  and  of  the 
alkaline  earths  are  soluble  in  water,  while  those  of  the  heavy 
metals  are  mostly  insoluble  in  water.     Regarding  their  solu- 
tion and  fusion,  see  page  112. 

2.  AgNO3,  argentic   nitrate,  precipitates    from    solutions 
of  ferricyanides   reddish-brown  Ag3Fe(CN)6,  argentic  ferri- 
cyanide, insoluble  in  nitric  acid,  soluble  in  ammonium  hy- 
droxide and  in  potassium  cyanide. 

3.  Ferrous    salts    (FeSO4,   ferrous    sulphate)    precipitate 
Fe3(Fe(CN)6)2,  ferrous  ferricyanide  (TurnbulPs  blue),  insolu- 
ble in  acids.     Ferric  salts  fail  to  produce  a  precipitate,  but 
cause  a  dark  coloration  ;  possibly  soluble  Fe2(Fe(CN)6)2,  ferric 
ferricyanide,  is  produced  : 

Fe2Cl6  +  2K3Fe(CN)6  =  Fe^F^CN)^  +  6KC1. 

4.  CuSO4,    cupric    sulphate,    precipitates    greenish-yellow 
Cu3(Fe(CN)6)2,  cupric  ferricyanide. 


81 


SULPHYDRIC   ACID,   H2S  (HYDROGEN   SULPHIDE). 

(Sulphydric  acid  combines  with  bases  to  form  salts  called 
sulphides.) 

Na^S,  sodium  sulphide,  may  be  employed  in  making  the  tests. 

1.  The    sulphides,    with   the   exception    of  those   of   the 
alkalies  and  of  the  alkaline  earths,  are  insoluble  in  water. 
Most  of  them  are  soluble  in  hydrochloric  and  in  nitric  acids ; 
some    are    soluble    only    in    nitro-hydrochloric    acid.      (See 
Sulphides  of  the  Heavy  Metals,  page  111.)     They  may  be 
recognized  by  their  giving  off  hydrogen  sulphide  when  dis- 
solved in  hydrochloric  acid,  or  by  the  separation  of  sulphur 
when  dissolved  in  nitric  acid  or  in  nitro-hydrochloric  acid. 

2.  AgNO3,  argentic  nitrate,  precipitates  black  Ag2S,  argen- 
tic sulphide,  soluble  in  nitric  acid  when  warmed. 

3.  Pb(C2H3O2)2,  plumbic  acetate,  precipitates  in  solutions 
of  sulphides  or  of  hydrogen  sulphide  black  PbS,   plumbic 
sulphide,  soluble  in  nitric  acid  when  warmed. 

4.  To  detect  hydrogen  sulphide  gas  a  strip  of  filter-paper 
is  moistened  with  plumbic  acetate  and  held  in  the  atmosphere 
containing  the  gas.     In  the  presence  of  hydrogen  sulphide 
the  paper  becomes  brown  or  black,  due  to  the  formation  of 
PbS,  plumbic  sulphide. 

5.  A  few  drops  of  an  alkaline  solution  of  plumbic  oxide 
(Pb(OK)2,  potassium  plumbite),  added  to  a  solution  contain- 
ing hydrogen  sulphide  or  a  sulphide  of  a  metal,  produces  a 
perceptible  brownish  coloration,  even  if  only  the  slightest 
trace  of  the  sulphide  be  present. 

6.  ]N"a2NOFe(CN)5,   sodium   nitro-prusside,    solutions   are 
colored  violet   by    sulphides,  but   not  by  solutions  of  free 
hydrogen  sulphide. 

7.  Many  of  the  sulphides  of  the  metals,  when  heated  in  a 
reduction-tube,    yield   a   sublimate  of  sulphur.      Sulphides, 


82 

heated  in  a  glass  tube  open  at  both  ends  and  held  obliquely 
in  the  flame,  are  oxidized,  with  the  formation  of  SO2,  sul- 
phurous anhydride.  Ignited  with  sodium  carbonate  in  the 
reducing  flame  on  charcoal,  they  yield  sodium  sulphide,  which, 
when  placed  on  a  clean  silver  coin  and  moistened  with  water, 
produces  a  black  discoloration  of  argentic  sulphide. 

NITROUS  ACID,   HNO2. 

(Nitrous  acid  combines  with  bases   to   form  salts  called 
nitrites.) 

KN02,  potassium  nitrite,  may  be  employed  in  making  the 
tests. 

1.  Most  of  the  nitrites  are  soluble  in  water.     Treated  with 
hydrochloric   or   sulphuric   acid   they   evolve    brownish-red 
fumes  of  NO2,  nitrogen  dioxide. 

2.  AgNO3,    argentic   nitrate,    precipitates   white   AgNO2, 
argentic  nitrite,  soluble  with  difficulty  in  water. 

3.  Pb(C2H3O2)2,  plumbic  acetate,  colors  solutions  of  nitrous 
acid  yellow. 

4.  H2S,  hydrogen  sulphide,  is  decomposed  by  nitrous  acid 
with  the  separation  of  sulphur : 

H2S  +  2HNO2  .=  2NO  +  S  +  2H2O. 

5.  FeSO4,  ferrous  sulphate,  added  to  a  solution  of  a  nitrite 
containing  a  few  drops  of  sulphuric  acid,(1)  produces  a  brown 
or  black  coloration,  due  to  the  formation  of  NO,  nitrogen 
monoxide,  which  enters  into  combination  with  the  ferrous 
sulphate : 

(a+3)FeSO4  +  H2SO4  +  2HNO,  =  *FeSO4(NO)2  + 

Fe2(S04)3  +  2H20. 
Heating  the  liquid  causes  the  coloration  to  disappear. 

1  The  nitrites  of  commerce  usually  contain  free  nitrous  acid,  and  there- 
fore respond  to  the  test  without  the  addition  of  sulphuric  acid. 


83 

6.  KI,  potassium  iodide,  (or  CdI2,  cadmium  iodide,)  starch 
paste,  and  dilute  sulphuric  acid,  added  to  a  solution  of  a 
nitrite,  immediately  produce  a  blue  coloration  in  the  liquid. 
The  nitrous  acid  liberates  iodine  from  the  hydriodic  acid  : 

2HNO2  +  2HI  =  2NO  +  2H2O  +  I2. 

The  free  iodine  combining  with  the  starch  forms  the  blue 
compound.  (In  this  test  cadmium  iodide  or  potassium  iodide 
free  from  iodic  acid  should  be  used,  as  hydriodic  and  iodic 
acid  undergo  decomposition  when  together,  with  the  liberation 
of  iodine  : 


HYPOCHLOROUS  ACID,  HC1O. 

(Hypochlorous    acid    combines  with   bases  to  form   salts 
called  hypochlorites.) 

NaCIO,  sodium  hypochlorite,  may  be  employed  in  making  the 


1 .  The  hypochlorites,  as  a  rule,  contain  chlorides,  produced, 
during  the  preparation  of  the  hypochlorite,  by  the  action  of 
the  chlorine  upon  hydroxides  : 

2NaOH  +  C12  =  NaCIO  +  NaCl  +  H2O. 
On    the   addition  of  acids   they  are   decomposed,  with  the 
evolution  of  chlorine : 

NaCIO  +  2HC1  =  NaCl  +  C12  +  H2O ; 

NaCIO  +  NaCl  +  H2SO4  =  Na2SO4  +  C12  -f  H2O. 

2.  AgNO3,  argentic  nitrate,  added  to  a  solution  of  a  hypo- 
chlorite produces  soluble  AgCIO,  argentic  hypochlorite,  which 
immediately  breaks  up  into  white,  insoluble  AgCl,  argentic 
chloride,  and  soluble  AgClO3,  argentic  chlorate : 

GAgCIO  —  2AgClO3  +  4AgCl. 

3.  Pb(C2H3O2)2,  plumbic  acetate,  produces  at  first  a  white 
precipitate  of  PbCl2,  plumbic  chloride,  which  soon  becomes 


84 


yellow  and  finally  brown,  due  to  the  formation  of  PbO2, 
lead  dioxide.  (In  like  manner  MnSO4,  manganous  sulphate, 
yields  brown  MnO(OH)2,  hydrated  peroxide  of  manganese.) 


FOURTH   GROUP. 

Acids  which  are  not  precipitated  by  barium  chloride  or  by 
argentic  nitrate  :  Nitric  Acid,  Chloric  Acid. 

NITRIC  ACID,   HNO3. 

(Nitric  acid  combines  with  bases  to  form  salts  called  nitrates.) 

KNOfr  potassium  nitrate,  may  be  employed  in  making  the 
tests. 

1.  The  nitrates,  with  the  exception  of  a  few  basic  salts,  are 
soluble   in  water.     Some   nitrates   (for   example,    Ba(NO3)2, 
barium  nitrate)  are  only  sparingly  soluble  in  nitric  acid. 

2.  BaCl2,  Pb(C2H3O2)2,  and  AgNO3  do  not  produce  pre- 
cipitates in  solutions  of  nitrates. 

3.  On  placing  a  small  crystal  of  FeSO4,  ferrous  sulphate, 
in  a  cooled  mixture  of   concentrated  sulphuric  acid  and  a 
solution  of  a  nitrate,  a  brownish-black  ring  is  formed  around 
the  crystal.     In  the  reduction  of  the  nitric  acid  NO,  nitrogen 
monoxide,  is   produced,  which    combines  with,   the   ferrous 
sulphate  to  form  an  unstable  compound  : 

(*+6)FeS04  +  3H2S04  +  2HNO3  =  [>FeSO4(NO)2]  + 

3Fe2(SO4)3  +  4H2O. 

The  test  is  best  made  in  a  flat  porcelain  dish,  or  in  a  watch- 
glass  placed  on  white  paper.     Heat  destroys  the  black  ring. 

4.  KI,  potassium  iodide,  (or  CdI2,  cadmium  iodide,)  starch 
paste,  and  dilute  sulphuric   acid,  added  to  a  solution  of  a 
nitrate,  produce  no  reaction  (distinction  from  nitrites),  but, 


85 

on  placing  a  fragment  of  zinc  in  the  liquid,  nitrous  acid  is 
evolved,  which,  acting  upon  the  potassium  iodide,  liberates 
the  iodine,  which  with  the  starch  produces  a  blue  coloration  : 

HN03  +Zn  +  H2S04  =  HNO2  +  ZnSO4  +  H2O  ; 

2HNO2  +  2HI  =  2NO  +  2H2O  +  I2. 
5.  Nitrates  of  the  alkalies  when  heated  in  a  reduction-tube 
are  reduced  to  nitrites,  with  the  evolution  of  oxygen  : 


The  nitrates  of  the  heavy  metals  when  heated  in  a  reduc- 
tion-tube evolve  reddish-brown  fumes  of  nitrogen  dioxide  : 

Pb(N03)2  =  PbO  +  0-1-  2N02. 

The  latter  reaction  also  takes  place  when  a  nitrate  of  an  alkali 
mixed  with  cupric  sulphate  is  heated  in  a  reduction-tube  : 

2KNO8  +  CuSO4  =  K2SO4  +CuO  +  O  +  2NO2. 
Nitrates  deflagrate  when  ignited  on  charcoal. 

CHLORIC  ACID,   HC1O3. 

(Chloric  acid   combines  with   bases  to  form   salts   called 
chlorates.) 


KQIOZ,  potassium  chlorate,  may  be  employed  in  making  the 
tests. 

1.  The  chlorates  are  soluble  in  water. 

2.  BaCl2,  barium  chloride,  does  not  produce  a  precipitate 
in  solutions  of  chlorates.     Pb(C2H3O2)2,  plumbic  acetate,  and 
AgNO3,  argentic  nitrate,  do  not  produce  precipitates  if  the 
solution  of  the  chlorate  be  free  from  chlorides. 

3.  On  warming  a  solution  of  a  chlorate  with  hydrochloric 
acid  the  liquid  becomes  greenish  yellow  in  color,  and  greenish- 
yellow  fumes  of  a  mixture  of  chlorine  and  C12O4,  chlorine 
tetroxide  (chlorine  peroxide),  are  evolved  : 

KC1O3  +6HC1  =  KC1  +  C18  +  3H2O  ; 

2KC1O3  +  4HC1  =  2KC1  +  C12O4  +  C12  +  2H2O. 


86 

4.  Concentrated  sulphuric  acid  poured  over  a  very  small 
piece  of  a  chlorate  in  a  porcelain  dish  causes  a  decomposition 
of  the  chlorate,  with  the  production  of  a  perchlorate  and 
chlorine  tetroxide  (chlorine  peroxide)  : 

3KC103  +  2H2S04  =  2KHS04  +  KC1O4  +  C12O4  +  H2O. 
Great  care  should  be  used  in  making  this  test,  and  only  small 
quantities  of  chlorate  should  be  employed.     Warming  should 
be  avoided,  as  explosions,  which  may  cause  personal  injury, 
are  likely  to  occur  on  the  application  of  heat. 

5.  Chlorates  heated  in  a  reduction-tube  undergo  decomposi- 
tion, and  are  converted  into  chlorides,  with  the  evolution  of 
oxygen  : 

KC1O3  =  KC1  +  Os. 

(Bromates  and  iodates  undergo  a  similar  decomposition  on 
being  heated,  forming  respectively  bromides  and  iodides,  with 
the  evolution  of  oxygen.) 

APPENDIX:    OEGANIC   ACIDS. 
Acetic  Acid,  Oxalic  Acid,  Tartaric  Acid. 

ACETIC  ACID,   HC2H302. 

(Acetic   acid   combines   with   bases   to   form   salts   called 
acetates.) 

NaC2H302,  sodium  acetate,  may  be  employed  in  making  the 
tests. 

1.  Most  of  the  acetates  are  easily  soluble  in  water. 

2.  BaCl2,    barium    chloride,   and    Pb(C2H3O2)2,    plumbic 
acetate,  do  not  produce  precipitates  in  solutions  of  acetates. 

3.  AgNO3  argentic   nitrate,   precipitates,  in   concentrated 
acetic  acid  or  in  concentrated  solutions  of  acetates,  crystalline 
AgC2H3O2,  argentic  acetate,  soluble  in  a  large  quantity  of 
water  and  in  ammonium  hydroxide. 


87 

4.  Fe2Cl6,  ferric  chloride,  added  to  a  neutral  acetate,  or  to 
acetic  acid,  which  must  afterwards  be  exactly  neutralized  with 
ammonium  hydroxide,  produces  a  reddish-brown  solution  of 
Fe2(C2H3O2)6,  ferric  acetate : 

6NaC2H302  +  Fe2Cl6  =  Fe2(C2H3O2)6  +  6NaCl. 

On   warming   this   solution   a   precipitate   of    brownish-red 

Fe2(OH)4(C2H3O2)2,  basic  ferric  acetate,  separates,  while  the 

supernatant  liquid  becomes  colorless  : 

Fe2(C2H302)6  +  4H20  =  Fe2(OH)4(C2H3O2)2  +  4HC2H3O2. 

5.  On  adding  sulphuric  acid  to  a  solution  of  an  acetate  and 
warming  the  liquid,  HC2H3O2,  acetic  acid,  is  liberated,  which 
may  be  recognized  by  its  odor  of  vinegar. 

6.  On  adding  C2H5OH,  alcohol,  to  a  cool  solution  of  an 
acetate  containing  sulphuric  acid  and  then  warming  the  liquid, 
C2H5C2H3O2,  ethyl  acetate  (acetic  ether),  is  produced,  which 
may  be  recognized  by  its  characteristic  apple-like  odor  : 

C2H5OH  +  H2S04  =  C2H5HS04  +  H2O ; 

C2H5HS04  -f  HC2H302  =  C2H5C2H302  +  H2SO4. 
The  alcohol  should  not  be  added  while  the  liquid  is  hot,  as 
violent  ebullition  might  occur  with  consequent  spurting  of  the 
liquid. 

7.  Acetates  on  being  ignited  are  decomposed,  without  the 
separation  of    carbon,  into  volatile  products  (for  example, 
acetone)  and  carbonates  or  oxides  of  the  metals  which  were 
in  combination  as  acetates. 

OXALIC  ACID,    H2C2O4. 

(Oxalic  acid  combines  with  bases  to  form  salts  called 
oxalates.) 

(J/VrJfZ4)2C204,  ammonium  oxalate,  may  be  employed  in  making 
the  tests. 

1.  Of  the  oxalates  those  of  the  alkalies  are  soluble  in 
water ;  most  of  the  others  are  insoluble  in  water. 


88 

2.  BaCl2,    barium   chloride,    precipitates   in   solutions   of 
neutral  oxalates  white  BaC2O4,  barium  oxalate,  easily  soluble 
in  hydrochloric  and  in  nitric  acid. 

3.  CaCl2,  calcium  chloride,  precipitates  from  neutral  solu- 
tions of  oxalates  white  CaCgO^  calcium  oxalate,  soluble  in 
hydrochloric  and  in  nitric  acid,  insoluble  in  acetic  acid. 

4.  Pb(C2H3O2)2,  plumbic  acetate,  precipitates  white  PbC2O4, 
plumbic  oxalate,  soluble  in  nitric  acid. 

5.  AgNO3,   argentic   nitrate,  precipitates   white  Ag2C2O4, 
argentic  oxalate,   soluble  in  nitric  acid  and  in  ammonium 
hydroxide. 

6.  Concentrated   sulphuric   acid,  on   being   warmed  with 
oxalic  acid  or  oxalates,  decomposes  them  into  water,  CO2, 
carbon  dioxide,  and  CO,  carbon  monoxide  : 

H2C2O4  +  H2SO4  ==  H2O  +  CO2  +  CO  +  H2SO4. 
On  pouring  the  gases  into  a  test-tube  containing  clear  solution 
of  calcium  hydroxide  (lime-water),  closing  the  tube  with  the 
thumb,  and  shaking  it,  the  production  of  a  milky  turbidity, 
due  to  the  formation  of  calcium  carbonate,  indicates  the 
presence  of  carbon  dioxide. 

7.  Oxalates  on  ignition  are  decomposed  into  carbon  mon- 
oxide and  carbonates  or  oxides  of  the  metals  which  were  in 
combination  as  oxalates.     Pure  oxalates  on  being  ignited  do 
not  become  black  in  color  : 


TARTARIC  ACID,  H2C4H4O6. 

(Tartaric  acid  combines  with  bases  to  form  salts  called 
tart  rates.) 

KNaC±HiO&,  potassium  sodium  tartrate,  may  be  employed 
in  making  the  tests. 

1.  The  tartrates  of  the  alkalies  and  some  of  the  tartrates 


89 

of  the  heavy  metals  are  soluble  in  water,  the  other  tartrates 
are  soluble  in  acids. 

2.  BaCl2,  barium   chloride,  added   in    excess   precipitates 
white  BaC4H4O6,  barium  tartrate,  soluble  in  hydrochloric  and 
in  nitric  acid. 

3.  CaCl2,  calcium   chloride,  added  in   excess    precipitates 
white,    crystalline   CaC4H4O6,    calcium   tartrate,    soluble    in 
hydrochloric,  nitric,  and  acetic  acids.     The  precipitate  is  also 
soluble  in  potassium  or  sodium  hydroxides,  forming  a  clear 
liquid,  from  which,  on  boiling,  the  calcium  salt  separates  in 
gelatinous  masses.     Probably  a  salt,  Ca~Na2C4H2O6,  is  pro- 
duced in  which  the  hydrogen  atoms  of  the  alcoholic  hydroxyl 
of  the  tartaric  acid  have  also  been  replaced  by  a  metal : 

CaC4H406  +  2NaOH  =  CaNa2C4H2O6  +  2H2O. 
This  compound,  on  being  boiled  with  considerable  water,  is 
reconverted  into  the  original  calcium  tartrate : 

CaNa2C4H206  +  2H2O  =  CaC4H4O6  +  2NaOH. 

4.  Pb(C2H3O2)2;     plumbic     acetate,     precipitates     white 
PbC4H4O6,  plumbic  tartrate,  soluble  in  nitric  acid  and   in 
ammonium  hydroxide. 

5.  AgNO3,  argentic   nitrate,  precipitates   in   solutions  of 
neutral   tartrates'  Ag2C4H4O6,    argentic   tartrate,    soluble   in 
nitric  acid  and  in  ammonium   hydroxide.     On  boiling  the 
precipitate  it  is  decomposed,  with  the  separation  of  metallic 
silver. 

6.  Tartrates  on  being  ignited  are  decomposed,  with  the 
production  of  an  odor  resembling  burnt  sugar,  the  separation 
of  carbon  and  the  formation  of  carbonates. 


III.    PRELIMINARY  EXAMINATION. 


(A)     PRELIMINARY  TESTS  IN   THE  DRY  WAY. 

THE  special  tests  for  bases  and  acids  (testing  in  the  Wet 
Way)  are  always  preceded  by  a  short  preliminary  examina- 
tion (in  the  Dry  Way),  in  order  to  obtain  general  information 
regarding  the  nature  of  the  substance  to  be  analyzed.  It  is 
hardly  possible  to  determine  the  best  method  to  be  employed 
in  the  preparation  of  the  substance  for  analysis  without  re- 
sorting to  this  preliminary  examination.  It  should  therefore 
never  be  omitted. 

When  solutions  are  to  be  analyzed,  a  portion  is  evaporated 
to  dryness  at  a  moderate  temperature  (without  ignition),  and 
the  residue  used  for  the  preliminary  tests. 

1.    EXAMINATION    IN   THE  REDUCTION-TUBE. 

To  ascertain  the  behavior  of  the  substance  at  higher  tem- 
peratures, a  small  portion  of  it,  or  of  the  residue  obtained  by 
evaporation,  is  placed  in  a  narrow  glass  tube  closed  at  one 
end,  and  heated,  at  first  slightly,  afterwards  more  strongly, 
and  then  to  redness. 

The  occurrence  of  any  of  the  following  changes  should 
especially  be  noted : 

1.  Separation  of  Carbon:  Indicates  the  presence  of  organic 
compounds.     Simultaneously  a  generation  of  empyreumatic 
vapors  takes  place,  or,  if  nitrogen   is   present,  an   odor  of 
burnt  feathers. 

2.  Elimination  of  Water :  Indicates  the  presence  of  water 
of    crystallization    or  of  adherent   moisture ;    frequently   a 

90 


91 

change  of  color  occurs,  as  in  the  transformation  of  the  blue 
hydrous  sulphate  of  copper  (CuSO4  -f  5H2O)  into  the  an- 
hydrous salt  (CuSO4).  Intumescence  may  take  place  as  in 
the  case  of  borax  (Na2B4O7  -j-  10H2O),  or  decrepitation  as  in 
sodium  chloride  (in  consequence  of  the  violent  expulsion  of 
water  confined  between  the  lamellae  of  the  crystals). 

3.  Change  in   Color:  Indicates  the  presence  of  combina- 
tions of  heavy  metals.     The  change  may  be  caused  by  the 
elimination  of  water  (see  2,  page  90),  or  by  the  conversion  of 
salts   into   oxides ;    for  example,   cupric  nitrate  and   cupric 
carbonate  become  black  in  color  when  heated,  due  to  their 
conversion  into  cupric  oxide  : 

Cu(NO3)2  =  CuO  -f  2NO2  +  O  ; 

CuCO3  =  CuO  +  CO2. 

Many  compounds  differ  in  color  when  hot  and  when  cold ; 
for  example,  oxide  of  zinc  is  yellow  when  hot  and  white 
when  cold. 

4.  Formation  of  a  Sublimate:  Indicates   the  presence  of 
volatile  compounds. 

(a)  White  sublimate :  Salts  of  mercury,  ammonium  salts, 
arsenious  oxide,  antimonious  oxide. — On  heating  the  sublimate 
with  dry  sodium  carbonate,  salts  of  mercury  become  red,  due 
to  the  formation  of  mercuric  oxide  (frequently  metallic  mer- 
cury is  produced  at  the  same  time)  ;  for  example  : 

HgCl2  +  NaaCOs  =  HgO  +  CO2  +  2NaCl. 

Ammonium  salts  evolve  ammoniacal  gas,  which  may  be 
recognized  by  the  odor,  and  by  its  coloring  moistened  tur- 
meric-paper brown,  and  red  litmus-paper  blue  : 

2NH4C1  -f-  ]Sa2C03  =  2NH3  +  CO2  -f  H2O  +  2NaCl. 

Arsenical  vapors  and  antimonious  oxide  are  apparently  not 
changed  when  heated  with  sodium  carbonate.  The  arsenic 
sublimes  in  octahedral  crystals;  the  antimony  forms  an 
amorphous  sublimate,  which  sometimes  contains  crystals. 


92 

(b)  Yellow  sublimate :  Mercuric  iodide  (becomes  red  when 
stirred),  arsenious  sulphide. 

(c)  Yellow  to  red :  Compounds  of  mercury  (formation  of 
basic  salts). 

(d)  Yellow  to  brownish  yellow  :     Sulphur  (when  hot  col- 
lects in  reddish-brown  drops).      Free  sulphur,  or  sulphides 
rich  in  sulphur, — for  example,  Sb2S5  =  Sb2S3  -f-  S2. 

(e)  Gray  to  black :  Mercury  (globules) ;  mercuric  sulphide 
(black,  red  when  rubbed) ;  iodine  (violet  vapors,  characteristic 
odor  of  iodine)  ;  arsenic  (mirror). 

It  is  to  be  remembered  that,  in  addition  to  the  sublimates 
mentioned,  quite  a  number  of  compounds  exist  which  are 
more  or  less  volatile, — for  example,  many  chlorides. 

5.  Evolution  of  Vapors : 

(a)  Colorless  vapors  should  be  tested   for  their  reaction 
with  litmus-paper.     The  acids  frequently  form  clouds  when 
escaping  from  the  tube  (in  consequence  of  their  changing  from 
the  anhydrous  to  the  hydrous  state). 

(b)  Reddish-brown   vapors :    Nitrogen   dioxide,   bromine. 
Nitrogen  dioxide,  resulting  from  the  decomposition  of  nitrates 
of   the   heavy   metals, — for    example,    Pb(NO3)2  =  PbO  -f 
2NO2  -j-  O,— does  not  color  starch-paper,  and  is  recognized 
by  its  odor.     Bromine,  also  recognizable  by  its  odor,  colors 
starch-paper  reddish  yellow. 

(c)  Violet  vapors  :  Iodine.    Characteristic  odor ;  frequently 
simultaneous  formation  of  a  black  sublimate.     Colors  starch- 
paper  blue  to  brownish  black. 

6.  Production  of  an  Odor : 

(a)  Odor  of  ammonia :  Ammonium  salts ;  compounds  of 
cyanogen  or  organic  compounds  containing  nitrogen. 

(b)  Odor  of  sulphurous  anhydride :    Resulting  from  the 
decomposition  of  sulphates. 

(c)  Odor  of  cyanogen :    Compounds  of  cyanogen.     Cyan- 


93 

ogen  gas  burns  when  ignited,  with  a  flame  pinkish  lavender 
in  color  : 


(d)  Odor  of  garlic  :  Compounds  of  arsenic,  resulting  from 
reduction. 

7.  Evolution  of  Oxygen  (may  be  recognized  by  the  flaring 
or  re-igniting  of  a  glowing  stick  held  at  the  mouth  of  the 
tube)  :  Indicates  the  presence  of  peroxides,  —  for  example, 
pyrolusite,  MnO2  : 

3MnO2  =  Mn3O4-f  O3; 
of  mercuric  oxide  : 

HgO  =  Hg  +  0; 
of  salts  rich  in  oxygen,  —  for  example  : 

KC1O3  =  KC1  +  O3. 

2.    EXAMINATION   ON   CHARCOAL. 

To  determine  the  behavior  of  substances  in  the  reducing 
flame  a  small  portion  of  the  substance,  generally  mixed  with 
dry  sodium  carbonate,  is  heated  in  a  cavity  in  the  charcoal  by 
means  of  the  reducing  flame  of  the  blowpipe.  (1)  The  sodium 
carbonate  is  added  in  order  to  transform  salts  and  sulphates 
into  carbonates  and  oxides  respectively,  —  for  example  : 

CaSO4  +  Na2CO3  =  CaCO3  -f  ]STa2SO4  ; 

CuCl2  -f  Na2CO3  =  CuO  +  COa  +  2NaCl. 
The  addition  of  sodium  carbonate  is  not  necessary  in  the  case 
of  metals  that  form  metallic  globules,  oxides,  and  salts  which 
are  easily  decomposed,  as  the  alkalies  and  their  salts  are  ab- 
sorbed by  the  charcoal  (because  of  their  easy  fusibility).    The 

1  The  reducing  flame  is  obtained  by  holding  the  blowpipe  near  the  flame 
and  by  gentle  blowing  directing  it  upon  the  substance  to  be  heated.  The 
oxidizing  flame  is  obtained  by  placing  the  blowpipe  in  the  interior  of  the 
flame  and  blowing  with  force. 


94 

oxides  of  the  remaining  elements  may  be  recognized  by  the 
following  characteristics  : 

1.  The  oxides  of  the  heavy  metals  heated  in  the  reducing 
flame  are  reduced  by  the  charcoal.  The  metals  themselves 
are  either  volatile  or  noil-  volatile,  may  oxidize  or  not,  and 
may  be  fusible  or  infusible  ;  therefore  fused  globules  may  be 
obtained,  or  infusible  masses  and  incrustations,  the  latter 
resulting  from  the  presence  of  metals  that  volatilize  and 
oxidize.  From  plumbic  oxide,  for  example,  metallic  lead  is 
obtained  : 


part  of  which  volatilizes,  combines  with  the  oxygen  of  the 
air,  and  is  deposited  on  the  cooler  part  of  the  charcoal  as  an 
incrustation  of  yellow  oxide  : 


The  metallic  globules  differ  in  their  behavior  in  the  oxi- 
dizing flame:  some  change  into  oxides  and  others  remain 
unchanged.  The  ductility  should  also  be  ascertained  ;  for 
this  purpose  the  globule  is  placed  in  a  mortar  and  struck  with 
the  pestle  ;  those  which  are  ductile  are  flattened  into  plates, 
while  those  which  are  brittle  break  into  pieces  and  may  be 
pulverized  by  subsequent  rubbing. 

(a)  Fused  metallic  globules,  without  incrustation,  are 
produced  : 

Yellow  :  gold,  ductile,  not  oxidizable. 
White  :  silver,  ductile,  not  oxidizable. 
Ked  :  copper,  (1)  ductile,  oxidizable. 
With  incrustation,  —  White  globule,  incrustation  yellow  : 
Ductile  :  lead,  oxidizable. 
Brittle  :  bismuth,  oxidizable. 
White  globule,  incrustation  white  : 

1  Generally  obtained  as  metallic  spangles. 


95 

Ductile:  tin,(1)  oxidizable. 
Brittle :  antimony,  oxidizable. 
(6)  Incrustation  without  metallic  globule  : 

White  (when  hot,  yellow  when  cold)  :  zinc. 
Yellowish  red  to  brown  :  cadmium. 

(c)  Gray,  infusible  masses  : 

Iron  "^ 

Cobalt 

Nickel 

Manganese   J 

Platinum  :  not  oxidizable. 

(d)  Neither  globule  nor  incrustation  : 

Volatile  with  odor  of  garlic :  arsenic. 
Volatile  without  odor  of  garlic  :  mercury. 

In  examining  metallic  globules  it  is  to  be  remembered  that 
in  the  presence  of  different  metals  alloys  may  be  formed. 

2.  White  infusible  masses  remain  on  the  charcoal  if  salts 
of  the  alkaline  earths,  magnesium  or  aluminium,  are  present. 
(By  the  action  of  Na2CO3,  carbonates  and  oxides  are  formed.) 
The  white  masses,  moistened  with  a  solution  of  cobaltous 
nitrate  and  strongly  heated  in  the  oxidizing  flame,  yield  as 
follows : 

Aluminium  :  blue  masses  (infusible). 

Magnesium :  pink-colored  masses. 

Barium       ^| 

Strontium    J>  gray  masses. 

Calcium     J 

1  Tin  and  antimony  are  obtained  with  difficulty  in  the  form  of  globules 
when  sodium  carbonate  is  employed.  Therefore  on  the  appearance  of  a 
white  incrustation  a  second  test  is  made,  in  which,  in  addition  to  sodium 
carbonate,  potassium  cyanide  is  added  to  the  salt,  and  the  whole  heated  in 
the  reducing  flame.  (KCN  thereby  changes  into  KCNO :  for  example, 
SnO2  -f  2KCN  =  Sn  +  2KCNO.)  Compare  also  its  behavior  with  cobalt 
solution,  see  6,  page  34. 


96 

The  cobaltous  nitrate  on  being  heated  is  converted  into  co- 
baltous  oxide : 

Co(NO3)2  =  CoO  +  2NO2  -f  O, 

which  combines  with  aluminium  and  magnesium  compounds. 
With  barium,  strontium,  and  calcium,  mixtures  only  of  the 
oxides  are  obtained. 

Many  silicates  and  phosphates  which  are  fusible  with  diffi- 
culty, and  also  many  borates  and  arseniates,  may  form  blue 
masses  when  ignited  with  cobaltous  nitrate ;  frequently  these 
double  salts  of  cobalt  are  easily  fusible. 

Zinc  oxide,  when  ignited  with  cobaltous  nitrate,  becomes 
yellowish  green  in  color ;  antimonious  oxide,  a  dirty  green ; 
stannic  oxide,  bluish  green.  (Compounds  of  CoO  are  pro- 
duced with  the  different  oxides.) 

3.  Green  fused  masses  (consisting  of  chromic  oxide)  indi- 
cate salts  of  chromium  and  chromates. 

4.  Yellow  or  brown  fused  masses,  consisting  of  sodium  sul- 
phide, indicate  the  presence  of  compounds  containing  sulphur. 
A  portion  is  placed  on  a  silver  coin  and  moistened  with  water 
to  ascertain  whether  a  black  discoloration  of  Ag2S  is  produced. 
(See  7,  page  81.)     As  the  formation  of  sodium  sulphide  by 
the  reduction  of  salts  containing  acids  of  sulphur  requires  time, 
and,  like  all  alkali  compounds,  the  sulphide  impregnates  the 
charcoal  on  continued  heating,  these  tests  must  be  made  just 
after  the  reduction  has  taken  place  and  before  the  sodium  sul- 
phide has  been  absorbed  by  the  charcoal. 

Many  of  the  compounds  containing  sulphur, — for  example, 
the  sulphides, — when  heated  in  a  small  glass  tube  open  at 
both  ends  and  held  obliquely  in  the  flame,  yield  sulphurous 
anhydride,  which  is  easily  recognized  by  its  odor. 


97 


3.    EXAMINATION    BY   MEANS  OF   MICROCOSMIC  SALT. 

A  portion  of  sodium  ammonium  phosphate  (microcosmic 
salt)  is  heated  in  a  loop  of  platinum  wire  until  it  melts,  and 
forms  a  bead.  A  very  small  portion  of  the  substance  to  be 
examined  is  then  attached  to  the  clear  bead,  which  is  again 
heated  in  the  oxidizing  flame  or  in  the  oxidizing  space  of  a 
Bunsen  flame.  The  ]STaNH4HPO4  -f  4H2O,  sodium  ammo- 
nium phosphate,  when  fused,  first  loses  its  water  of  crystal- 
lization and  then  changes  into  sodium  metaphosphate : 

NaNH4HPO4  ==  NaPO3  -f  H2O  +  NH3. 
Th^  sodium  metaphosphate  dissolves  most  of  the  oxides 
and  salts  (in  the  latter  a  replacement  of  the  acids  takes  place), 
and  forms  beads,  generally  characteristic  in  color : 
CuO  -f  NaP03  =  CuNaP04 ; 
CuSO4  -f  JSTaPO3  =  CuNaPO4  +  SO3. 

Some  of  the  beads  change  color  in  the  reducing  flame  or  in 
the  reducing  space  of  the  Burisen  flame  (in  consequence  of  the 
reduction  of  the  phosphates) ;  for  example,  the  transparent 
bluish-green  copper  bead  by  reduction  becomes  brownish-red 
and  opaque : 

CuNaPO,  +  C  =  NaP03  +  Cu  +  CO  ; 

the  violet  manganic  oxide  bead  in  the  reducing  flame  is  con- 
verted into  the  colorless  manganous  bead  : 

Mn2(NaPO4)3  -f  C  =  2MnNaPO4  +  NaPO3  +  CO. 
Borax  (Na2B4O7  -f  10H2O)  with   oxides  and  salts   yields 
beads  similar  to  microcosmic  salt,  which  are  likewise  reducible  : 
Na2B4O7  -f  CuO  =  2NaBO2  +  Cu(BO2)2 ; 
Na2B4O7  +  CuSO4  =  2NaBO2  +  Cu(BO2)2  +  SO3 ; 
2NaBO2  -f  Cu(BO2)2  +  C  =  Na2B4O7  +  Cu  +  CO. 
The  reduction  of  the  oxide  in  the  beads  is  often  facilitated 
by  adding  a  small  piece  of  tin  foil : 

2Cu]SaPO4  +  Sn  =  Sn(NaPO4)2  +  Cu2. 

E         g 


98 

The  following  elements(1)  produce  characteristic  colorations 
in  the  bead  of  microcosmic  salt : 

Oxidizing  Flame.  Reducing  Flame. 

Iron  :  yellow  to  dark  red  when      Green  to  colorless, 
hot,    light   yellow   to 
colorless  when  cold. 

Nickel :          same  as  iron.  As  in  the  oxidizing  flame.(2) 

Cobalt :          blue.  Blue. 

Manganese :  violet.  Colorless. 

Chromium :  green.  Green. 

Copper :         blue-green.  Brownish,  opaque. 

The  remaining  oxides  yield  colorless,  transparent  or  .trans- 
lucent, enamel-like  beads. 

The  behavior  of  silicic  acid  and  of  the  silicates  in  the  bead 
of  microcosmic  salt  is  characteristic.  Silicic  acid  does  not 
dissolve  in  the  bead,  but,  while  the  bead  is  in  a  state  of  fusion, 
swims  in  distinctly  outlined  masses.  The  silicates  are  decom- 
posed in  the  bead,  with  the  separation  of  undissolved  silicic 
acid : 

NaPO3  +  CaSiOj  =  CaNaPO4  +  SiO2. 

4.    EXAMINATION   IN   THE   FLAME. 

If  the  presence  of  alkalies  or  alkaline  earths  is  suspected, 
a  small  portion  of  the  substance,  or  of  the  residue  obtained  by 
evaporation,  is  attached  to  a  loop  of  dean  platinum  wire/3) 
moistened  with  a  drop  of  hydrochloric  acid,  and  held  in  the 
flame  of  a  Bunsen  burner. 

The  flame  is  colored  by  the  salts  of 
Potassium :  violet. 
Sodium :  intense  yellow. 

*For  beads  produced  by  the  rare  elements,  see  Appendix. 

2  For  the  behavior  of  nickel  in  the  borax  bead,  see  7,  page  49. 

3  Or  the  wire  may  be  dipped  in  the  concentrated  solution  of  the  sub- 
stance to  be  examined. 


99 

Barium  :  green. 
Strontium :  crimson. 
Calcium :  yellowish  red. 

It  must  be  remembered  that,  if  two  or  more  of  these  ele- 
ments are  present,  one  colored  flame  may  interfere  with  the 
other. 

Salts  of  copper  and  also  boric  acid  color  the  flame  green. 
For  colored  flames  produced  by  the  rare  elements,  see  Ap- 
pendix. 


(B)    PRELIMINARY  TESTS   FOR  ACIDS. 

Important  conclusions  regarding  the  presence  or  absence 
of  certain  acids  may  be  drawn  from  the  behavior  of  their  salts 
with  dilute  and  concentrated  sulphuric  acid,  and  also  with 
alcohol  and  sulphuric  acid. 

1.  If  a  portion  of  the  substance  or  solution  be  placed  in  a 

test-tube  and  dilute  sulphuric  acid  poured  over  it,  there  may 

be  evolved : 

Colored    Gases:     Greenish-yellow   chlorine   in   presence   of 
hypochlorites  (see  1,  page  83).     Moistened  potassium 
iodide  starch  paper  held  in  the  fumes  is  colored  blue. 
Red  vapors  of  nitrogen  dioxide  from  nitrites  (see  1,  page 
82). 

Colorless  Gases  recognized  by  their  Odor :  Sulphurous  an- 
hydride, from  sulphites  or  hyposulphites;  in  the 
presence  of  the  latter,  separation  of  sulphur  also  takes 
place  (see  2,  page  63).  Detection  of  sulphurous  an- 
hydride by  potassium  iodate  (see  2,  page  61). 
Hydrocyanic  acid,  from  many  of  the  cyanides,  recognized 
by  its  odor  of  bitter  almonds,  and  also  by  the  sulpho- 
cyanide  reaction  (see  5,  page  78). 


100 

Acetic  acid  in  presence  of  acetates. 

Hydrogen  sulphide,  from  many  of  the  sulphides,  blackens 
paper  saturated  with  solution  of  plumbic  acetate  (see 
4,  page  81).  Polysulphides  evolve  hydrogen  sul- 
phide, with  the  separation  of  sulphur;  sulpho-acids 
may  also  separate.  (See  pages  121,  122.) 
Colorless  and  Odorless  Gas :  Carbon  dioxide  is  liberated  with 
effervescence  from  carbonates  (to  be  confirmed  with 
calcium  hydroxide,  see  2,  page  68). 

2.  If  a  small  portion  of  the  substance  is  treated  with  three 
or  four  times  its  volume  of  concentrated  sulphuric  acid  and 
gently  warmed,  there  may  be  evolved  : 

Colored  Gases :  Greenish-yellow  chlorine  in  presence  of  hypo- 
chlorites;  also  when  both  chlorides  and  nitrates,  or 
chlorides  and  peroxides  are  present.  (When  chlorides 
and  nitrates  are  present,  hydrochloric  acid  and  nitric 
acid  are  simultaneously  liberated  and  react  upon  each 
other  (see  d,  page  106).  When  chlorides  and  per- 
oxides are  present,  the  liberated  hydrochloric  acid  acts 
upon  the  peroxides  (see  c,  page  106).) 
Greenish-yellow  explosive  mixture  of  chlorine  and  chlo- 
rine tetroxide,  derived  from  chlorates  (see  4,  page 
86). 

Brownish  bromine  together  with  hydrobromic  acid  de- 
rived from  bromides ;  the  gas  colors  starch  paper  red- 
dish yellow. 
Brownish-red  chromium  oxychloride  when  chlorides  and 

chromates  are  both  present  (see  4,  page  74). 
Reddish-brown  fumes  indicate  nitrites  (see  1,  page  82). 
Violet  vapors  of  iodine  from   iodides  color  moistened 

starch  paper  blue. 
Colorless  Gases  recognized  by  their  Odor:  Hydrochloric  acid 


101 

vapors  from  chlorides;  pungent  odor,  and  render 
argentic  nitrate  solution  (on  glass  rod)  turbid  (see  2, 
page  73). 

Hydrobromic  acid  (see  above). 

Hydrofluoric  acid  from  fluorides ;  of  a  strongly  acid 
odor,  etches  glass  (see  4,  page  67). 

Nitric  acid  from  nitrates,  pungent  odor.  Red  vapors 
arise  when  ferrous  sulphate  is  added. 

Sulphurous  anhydride  from  sulphites  and  hyposulphites 
(see  2,  page  61,  and  2,  page  63. — N.B.  May  also  result 
from  the  reduction  of  the  sulphuric  acid  employed). 

Hydrogen  sulphide  from  sulphides  (see  4,  page  81). 

Acetic  acid  from  acetates,  odor  of  vinegar  (see  5,  page 

87). 

Colorless  and  Odorless  Gases:   Oxygen  (recognized  by  test 
with  glowing  wood,  see  7,  page  93)  in  presence  of  per- 
oxides, chromates,  and  permanganates ;  for  example  : 
Mn02  +  H2SO4  =  MnS04  +  H2O  +  O  ; 
2K2CrO4  +  5H2SO4  =  Cr2(SO4)3  -f-  2K2SO4  +  5H2O 

+  03; 

2KMnO4  -f  3H2SO4  =  2MnSO4  +  K2SO4  +  3H2O 
+  0, 

Chromates  become  green  in  color;  permanganates  are 
decolorized. 

Carbon  dioxide  from  carbonates,  effervescence  (see  2, 
page  68). 

Carbon  monoxide  (burns  with  bluish  flame)  from  organic 
substances,  usually  with  blackening  of  the  substance 
and  the  evolution  of  carbon  dioxide  and  sulphurous 
anhydride,  as  in  the  case  of  tartaric  acid.  Carbon 
monoxide  together  with  carbon  dioxide  is  evolved 
from  oxalic  acid  (without  blackening,  see  6,  page  88). 
From  cyanides,  ferrocyanides,  etc.  (Cyanides,  page  110). 

9* 


102 

In  presence  of  the  latter  a  transitory  bluish  coloration 
appears. 

3.  If  a  portion  of  the  substance  is  heated  with  concentrated 
sulphuric  acid  and  alcohol,  there  is  produced,  in  the  presence 
of  acetates,  ethyl  acetate,  Avhich  may  be  recognized  by  its 
apple-like  odor  (see  6,  page  87).  If  the  alcohol  is  ignited,  the 
flame  assumes  a  green  color  in  presence  of  boric  acid  (see 
5,  page  66). 


IV.  SOLUTION  AND  FUSION. 


SOLIDS  must  necessarily  be  in  solution  in  order  to  make  the 
tests  in  the  Wet  Way.  The  method  employed  in  dissolving 
the  solid  depends  upon  the  nature  of  the  substance;  with 
this  in  view,  substances  may  be  divided  into  the  following 
five  groups : 

1.  Oxides  and  salts  (in  general). 

2.  Metals  and  alloys. 

3.  Sulphides  (of  the  heavy  metals). 

4.  Cyanides  (of  the  heavy  metals). 

5.  Silicates. 

A  distinction  may  be  made  between  solution  and  fusion. 
Many  salts  cannot  be  directly  dissolved  in  water  or  acids, 
but  must  undergo  a  special  treatment  to  separate  the  acids 
from  the  bases,  as  in  the  case  of  barium  sulphate ;  the  sul- 
phuric acid  is  separated  from  the  barium  by  fusing  with 
sodium  carbonate.  By  fusion,  new  compounds  of  the  bases 
and  acids  are  obtained  which  are  soluble  in  water  or  acids. 

In  case  a  substance  is  not  entirely  soluble  in  any  one  of 
the  solvents,  it  should  be  treated  by  each  solvent  in  turn,  and 
the  solutions  analyzed  separately,  as  two  simple  analyses  are 
more  quickly  made  than  one  complex  one.  For  example,  the 
substance  is  first  boiled  with  water,  the  solution  obtained  is 
filtered  off  and  set  aside  for  examination,  any  residue  insoluble 
in  hot  water  is  treated  with  nitric  acid  and  the  solution  ex- 
amined separately,  any  residue  remaining  after  treatment  with 
nitric  acid  is  treated  with  hydrochloric  acid.  By  this  pro- 

103 


104 

cedure  a  more  distinct  insight  into  the  nature  of  the  sub- 
stance to  be  analyzed  is  obtained. 

Hard  bodies,  minerals,  etc.,  must  be  pulverized  in  a  por- 
celain or  agate  mortar  before  they  are  dissolved.  Very  hard 
minerals  are  first  crushed  in  a  steel  mortar,  and  the  coarse 
powder  thus  obtained  is  afterwards  pulverized  in  an  agate 
mortar.  It  is  advisable  to  sift  the  powder  through  a  linen 
cloth  (previously  washed  and  dried),  remove  the  coarser 
particles  and  again  pulverize  them,  and  repeat  the  operation. 

If  the  substance  to  be  analyzed  be  an  organic  compound 
or  contain  organic  material  (as  shown  by  the  preliminary  ex- 
amination), the  organic  substance  must  be  destroyed  by  igni- 
tion and  the  residue  then  dissolved  in  water  (removing  by 
filtration  any  separated  carbon). 

1.    DISSOLVING  OXIDES  AND  SALTS. 

(a)  A  portion  of  the  substance  to  be  dissolved  is  heated 
in  a  test-tube,  with  water.  In  case  it  enters  into  solution,  a 
larger  portion  is  dissolved  and  the  liquid  employed  in  testing 
for  bases  and  acids.  If  the  substance  is  apparently  undis- 
solved,  it  is  separated  by  filtration  and  the  filtrate  evaporated 
to  dryness,  to  ascertain  whether  any  of  the  original  substance 
entered  into  solution. 

(6)  Substances  insoluble  in  water  are  further  tested  as  to 
their  solubility  in  dilute  nitric  acid.  An  excess  of  nitric  acid 
should  be  avoided,  as  many  nitrates  soluble  in  water  are 
insoluble  in  excess  of  strong  acids. 

On  dissolving  oxides  with  nitric  acid,  nitrates  are  formed, 
and  on  dissolving  salts,  nitrates  of  the  bases  are  produced 
with  the  liberation  of  the  acids  which  were  in  combination ; 
for  example : 

Ca3(P04)2  +  6HNOS  *=  3Ca(NO3)2  +  2H3PO4 ; 
CuC03  +  2HX03  -  Cu(X03)2  +  CO2  +  H2O. 


105 

Thus  the  presence  of  volatile  acids  becomes  evident : 

Carbonic  acid :  effervesces  ;  odorless  gas  ;  renders  calcium 

hydroxide  solution  turbid  (see  2,  page  68). 
Hydrocyanic  acid :  odor  of  bitter  almonds ;  forms  am- 
monium sulphocyanide  with  ammonium  sulphide  (see 
5,  page  78). 

Hydrogen  sulphide  :  recognizable  by  its  odor ;  blackens 
paper  saturated  with  solution  of  plumbic  acetate  (see 
4,  page  81). 

Sulphurous  acid  :  odor  of  burning  sulphur ;  colors  potas- 
sium iodate  starch  paper  blue  (see  2,  page  61). 
Under  certain  conditions  the  presence  of  iodine,  bromine, 
or  chlorine  may  become  evident  (see  2,  page  100). 

In  using  nitric  acid  as  a  solvent,  acids  which  are  soluble 
with  difficulty  may  separate  :  Boric  acid,  crystalline,  easily 
soluble  in  hot  water ;  silicic  acid,  gelatinous. 

Reddish-brown  fumes  of  nitrogen  dioxide  result  from  the 
processes  of  oxidation ;  for  example,  when  mercurous  com- 
pounds are  converted  into  mercuric  compounds  : 

Hg20  +  6HN03  =  2Hg(N03)2  +  2NO2  +  3H2O. 
These  oxidations  may  interfere  with  the  results  of  the  analysis, 
especially  when  compounds  of  mercury  are  present.  After 
the  oxidation  with  nitric  acid  it  is  impossible  to  determine  the 
original  condition  of  oxidation  of  the  salt ;  for  example,  in 
the  case  of  mercury,  after  oxidation  it  cannot  be  ascertained 
whether  the  salt  was  present  originally  as  a  mercurous  or 
a  mercuric  salt.  Salts  of  mercury  which  are  insoluble  in 
water  or  in  moderately  warm  dilute  nitric  acid  are  decom- 
posed by  boiling  in  sodium  hydroxide  (compare  page  106, 
e).  Compounds  of  arsenic  should  be  dissolved,  when  pos- 
sible, in  hydrochloric  acid,  in  order  to  prevent  the  conver- 
sion of  arsenious  acid  into  arsenic  acid.  Plumboso-plumbic 
oxide  (red  lead)  when  treated  with  dilute  nitric  acid  is  decom- 


106 

posed  into  soluble  plumbic  nitrate  and  insoluble,  brown  lead 
dioxide  : 

Pb3O4  -f  4HNO3  =  2Pb(NO3)2  +  PbO2  -f  2H2O. 
The  latter  is  converted  into  plumbic  chloride  by  concentrated 
hydrochloric  acid. 

(c)  Those  substances  which  are  insoluble  in  dilute  nitric 
acid  must  be  treated  with  concentrated  hydrochloric  acid.  If 
in  dissolving  the  substance  in  hydrochloric  acid  chlorine  gas 
is  evolved,  peroxides  and  similar  compounds,  such  as  manga- 
nese dioxide,  chromic  acid,  or  permanganic  acid,  are  present  : 


2CrO3  +  12HC1  =*  O2C16  +  C16  +6H2O  ; 

Mn2O7  -f  14HC1  =  2MnCl2  +  C110  +  7H2O. 
Lead  dioxide  is  converted  into  plumbic  chloride,  which  crys- 
tallizes as  the  solution   cools  ;    it  is   best  decomposed  with 
sodium  carbonate  (page  106,  e). 

(d)  Many  compounds  insoluble  in  nitric  acid  or  in  hydro- 
chloric acid  are  soluble  in  nitro-hydrochloric  acid  (aqua  regia). 

In  dissolving  with    nitro-hydrochloric   acid   chlorine(l;  is 
liberated,  which  is  the  active  agent  in  effecting  solution  : 

3HC1  +  HNO3  =  C13  +  NO  +  2H2O. 

Nitro-hydrochloric  acid  is  prepared  by  mixing  about  three 
volumes  of  concentrated  hydrochloric  acid  with  one  volume 
of  concentrated  nitric  acid  ;  the  reaction  takes  place  upon  the 
application  of  heat.  When  nitro-hydrochloric  acid  is  em- 
ployed as  a  solvent,  oxidation  necessarily  occurs  if  the  sub- 
stance is  capable  of  being  oxidized,  as,  for  example,  with 
compounds  of  mercury. 

(e)  Many  compounds  that  are  insoluble  in  water  and  in 
acids  are  decomposed  by  boiling  or  fusing  with  carbonates  of 
the  alkalies,  —  that  is,  they  are  converted  into  soluble  com- 

1  Besides  (NOC1)  nitrosyl  chloride  and  (NO2C1)  nitroxyl  chloride. 


107 

pounds.  Among  them  are  plumbic  sulphate,  the  sulphates 
of  the  alkaline  earths,  plumbic  chloride,  plumbic  iodide, 
stannic  oxide,  etc. 

Of  the  sulphates,  plumbic  sulphate  and  calcium  sulphate 
are  easily  decomposed  by  boiling  in  a  solution  of  sodium 
carbonate.  Precipitated  strontium  sulphate  is  also  decom- 
posed in  the  same  manner,  although  with  more  difficulty. 
Precipitated  barium  sulphate  is  only  partly  decomposed  by 
boiling  with  sodium  carbonate  solution.  These  sulphates  (as 
well  as  minerals)  are  readily  decomposed  by  being  fused  with 
from  four  to  six  parts  of  sodium  potassium  carbonate.^  In 
these  decompositions  the  acid  of  the  substance  fused  unites 
with  the  alkalies,  and  the  base  is  converted  into  a  carbonate ; 
for  example,  with  BaSO4  and  NaKCO3  the  compounds 
NaKSO4,  soluble  in  water,  and  BaCO3,  soluble  in  acids,  are 
formed : 

NaKCO3  +  BaSO4  =  NaKSO4  +  BaCO3. 

The  fused  mass  is  completely  extracted  with  hot  water  and 
the  insoluble  residue  (after  separation  by  filtering)  is  dissolved 
in  hydrochloric  acid  or  nitric  acid.  The  aqueous  solution  is 
to  be  examined  for  the  acid,  and  the  acid  solution  for  the 
base. 

Plumbic  chloride  and  plumbic  iodide,  etc.,  when  boiled 
with  a  solution  of  sodium  carbonate,  are  decomposed  respec- 
tively into  chloride  and  iodide  of  sodium  and  plumbic 
carbonate : 


1  The  double  salt  NaKCO3  fuses  more  easily  than  the  sodium  or  potas- 
sium salt  alone.  The  fusion  is  best  made  in  a  platinum  crucible,  as 
porcelain  is  attacked  by  the  alkali  carbonates.  The  following  substances 
should  never  be  fused  in  a  platinum  crucible  :  potassium  and  sodium 
hydroxide,  nitrates  and  cyanides  of  the  alkalies,  metals  and  metallic 
sulphides,  or  any  substance  from  which  a  metal  may  be  obtained  by 
reduction  or  substances  from  which  chlorine  may  be  evolved. 


108 

PbCl2  +  Na2CO3  =  2NaCl  +  PbCO3. 
(Plumbic  carbonate  is  slightly  soluble  in  sodium  carbonate.) 

Stannic  oxide  (cassiterite)  when  fused  with  a  carbonate  of 
an  alkali  is  converted  into  a  stannate  of  the  alkali,  which  is 
soluble  in  water  and  in  hydrochloric  acid : 

SnO2  +  K2CO3  =  SnO(OK)2  +  CO2 ; 
SnO(OK)2  +  6HC1  =  SnCl4  +  2KC1  +  3H2O. 
Fusion  is  continued  until  carbon  dioxide  ceases  to  be  evolved. 
As  stannic  oxide  is  acted  upon  only  with  great  difficulty  by 
sodium  carbonate,  it  is  best  fused  in  a  silver  crucible  with 
sodium  or  potassium  hydroxide,(1;  and  the  fused  mass  treated 
with  water  and  hydrochloric  acid,  as  mentioned  above. 

Many  substances  are  unacted  upon  by  the  carbonates  of 
the  alkalies,  but  are  readily  decomposed  on  being  foiled  with 
sodium  or  potassium  hydroxide ;  for  example,  mercury  and 
silver  compounds.  An  oxide  of  the  metal  is  formed,  while 
{he  acid  remains  in  solution  in  combination  with  the  alkali. 
The  oxide  after  being  washed  is  dissolved  in  nitric  acid. 
Hg2Cl2  -f  2NaOH  =  Hg2O  -f  2XaCl  +  H2O. 

In  dissolving  compounds  of  mercury  cold  dilute  nitric  acid 
should  be  used,  in  order  to  avoid  the  oxidation  of  mercurous 
salts  to  mercuric  salts.  (Mercuric  iodide,  which  partly  redis- 
solves  in  a  carbonate  of  an  alkali, — i.e.,  in  the  iodide  of  the 
alkali  which  is  formed, — should  be  dissolved  in  nitro-hydro- 
chloric  acid.) 

(/)  Compounds  of  fluorine  (for  example,  fluor  spar)  are 
decomposed  by  being  gently  heated  with  concentrated  sul- 
phuric acid  in  a  platinum  crucible  : 

1  Or  it  may  be  fused  in  a  porcelain  crucible  with  three  parts  of  sodium 
carbonate  and  three  parts  of  sulphur  to  one  part  of  the  substance,  and  the 
fused  mass,  after  cooling,  extracted  with  water.  The  yellow  solution  con- 
tains the  tin  as  sulphostannate,  Na2SnS3 ;  the  insoluble  residue,  containing 
sulphides,  is  to  be  examined  further  according  to  3,  page  111. 


109 

CaF2  +  H2S04  -  CaS04  +  2HF. 

The  hydrofluoric  acid  is  recognized  by  its  etching  glass  (see 
4,  page  67);  the  residue  in  the  crucible,  consisting  of  sul- 
phates, is  dissolved  in  hydrochloric  acid  or,  if  necessary, 
fused  with  sodium  carbonate. 

Silicates  containing  fluorine,  if  treated  in  this  manner, 
yield  silicon  fluoride,  according  to  the  reaction  : 

2CaF2  +  SiO2  H-  2H2SO4  =  SiF4  +  2CaSO4  +  2H2O. 
If  the  evolved  gas  be  conducted  through  a  glass  tube  moist- 
ened with  water,  silicic  acid  together  with  hydrofluosilicic  acid 
is  produced : 

3SiF4  +  3H20  =  2H2SiF6  +  H2SiO3. 

The  silicic  acid  will  appear,  either  directly  or  on  drying  the 
tube,  in  the  form  of  a  white  coating  (see  5,  page  68). 

(g)  Chromic  oxide,  chromite,  aluminium  oxide,  and  ferric 
oxide  are  best  fused  by  mixing  them  with  ten  parts  of  acid 
potassium  sulphate.     If  the  heat  applied  is  not  too  great, 
neutral  sulphates  (together  with  basic  salts)  are  formed  : 
A1203  +  6KHS04  ±*  A12(S04)3  +  3K2SO4  +  3H2O, 
which,  on  cooling,  may  be  dissolved  by  water  or  hydrochloric 
acid. 

Chromite  is  best  fused  with  acid  potassium  sulphate,  and 
the  fused  mass  obtained  again  fused  with  potassium  chlorate 
and  potassium  carbonate,  to  convert  the  chromic  oxide  into 
chromic  acid  : 

Cr2(S04)3  +  3K2C03  =  Cr2O3  +  3K2SO4  +  3CO2 ; 

Cr2O3  +  2K2CO3  +  KC1O3  =  2K2CrO4  +  KC1  +  2CO2. 
The  fused  mass  yields  potassium  chromate  when  extracted 
with  water ;  the  residue,  consisting  of  ferric  oxide  (with  some 
chromic  oxide)  is  dissolved  in  hydrochloric  acid. 

(h)  Carbon  (charcoal,  graphite)  and  sulphur  are  recognized 
by  their  appearance  and  their  behavior  when  heated. 

10 


110 

2.    THE   DISSOLVING  OF  METALS  AND  ALLOYS. 

Metals  and  alloys  are  treated  with  concentrated  nitric  acid 
and  heated  until  red  vapors  cease  to  be  produced  upon  the 
further  addition  of  acid.  The  excess  of  nitric  acid  (which 
would  interfere  with  the  solubility  of  the  nitrates  in  water)  is 
evaporated  on  the  water-bath,  and  the  residue  dissolved  with 
water  and  a  little  nitric  acid.  Most  of  the  metals  enter  into 
solution  as  nitrates,  gold,  platinum,  etc.,  remain  unchanged, 
and  tin  and  antimony  remain  as  oxides  or  hydroxides.u) 

In  the  'presence  of  tin  or  antimony  arsenic  may  be  found 
in  the  residue,  in  the  arsenic  condition.  The  residue,  after 
thorough  washing,  is  digested  with  yellow  ammonium  sul- 
phide, whereby  tin,  antimony,  and  arsenic  enter  into  solution 
as  sulpho-salts : 

.  Sn(OH)4  -f  3(NH4)2S  =  (NH4)2SnS3  +  4NH3  +  4H2O ; 
Sb2O3  +  6(NH4)2S  +  S2  =  2(NH4)3SbS4  +  6NH3  +  3H2O ; 
Sb2O4  +  7(NH4)2S  +  S  —  2(NH4)3SbS4  +  8NH3  -f-  4H2O ; 
Sb2O5  +  8(NH4)2S  =  2(NH4\SbS4  +  10NH3  -f  5H2O ; 
AsA  +  8(NH4)2S  =  2(NH4)sAsS4  +  10NH3  +  5H2O. 
If  an  insoluble  residue  remain,  it  is  again  treated  with 
nitric  acid  ;  if  it  still  fail  to  dissolve,  it  is  finally  treated  with 
nitro-hydrochloric  acid,  which  dissolves  gold  and  platinum 
as  chlorides : 

Au  -f-  3HC1  -|-  HNOS  =  AuCls  -f-  NO  -f  2H2O ; 
3Pt  +  12HC1  +  4HNO3  =  3PtCl4  +  4NO  +  8H2O. 

1  In  dissolving  metals  in  nitric  acid  different  oxides  of  nitrogen  are  pro- 
duced, depending  upon  the  concentration  of  the  acid  employed.  With 
nitric  acid  of  1.42  specific  gravity  NO2  is  produced  ;  with  an  acid  of  1.35 
specific  gravity,  principally  N2O3;  with  an  acid  of  1.2  specific  gravity 
NO ;  and  with  an  acid  of  1.1  specific  gravity  N2O.  (With  an  acid  of 
greater  dilution  ammonia  is  produced.)  Nitric  acid  of  1.1  or  less  specific 
gravity  is  decomposed  only  by  the  more  strongly  positive  metals ;  for 
example,  Zn  and  Fe. 


in 


3.  SULPHIDES  OF  THE  HEAVY  METALS. 

The  sulphides  of  the  heavy  metals  generally  possess  a 
metallic  lustre ;  like  the  metals  they  are  treated  with  concen- 
trated nitric  acid,  whereby  most  of  them  are  dissolved  as 
nitrates : 

CuS  +  4HNO3  —  Cu(NO3)2  +  S  +  2NO2  +  2H2O. 
The  procedure  is  as  given  under  2,  page  110.  The  sulphur 
which  separates  first  is  oxidized  by  the  nitric  acid  to  sulphuric 
acid.  The  insoluble  residue,  in  addition  to  the  oxides  of  tin, 
antimony,  and  arsenic,  may  contain  PbSO4,  BiONO3  (formed 
on  treating  the  nitrate  with  water),  and  HgS.  This  residue 
is  treated  with  yellow  ammonium  sulphide,  which  dissolves 
tin,  antimony,  and  arsenic.  Any  residue  remaining  is  filtered 
off  and  treated  with  nitric  acid  to  dissolve  the  lead  and  bis- 
muth (which  at  this  stage  may  be  found  again  as  sulphides), 
and  any  residue  of  mercuric  sulphide  is  collected  on  a  filter 
and  dissolved  by  nitro-hydrochloric  acid : 
3HgS  +  6HC1  +  2HNO3  =  3HgCl2  +  2NO  +  4H2O  -f  S3. 
Finally  silicious  gangue,  barite,  etc.,  may  remain,  which 
should  be  examined  according  to  5  (page  113)  and  1  (page 
104)  respectively. 

The  sulphides  are  easily  recognized  by  their  appearance, 
and  also  by  their  behavior  in  the  preliminary  examination. 

4.    CYANIDES. 

The  simple  cyanides,  which  are  insoluble  in  water,  may  be 
decomposed  into  chlorides  and  hydrocyanic  acid,  by  boiling 
with  concentrated  hydrochloric  acid. 

Argentic  cyanide  and  mercuric  cyanide,  in  which  the  cyan- 
ogen cannot  be  detected  by  the  ordinary  methods,  may  be 
readily  recognized  by  their  behavior  when  heated,  as  they 
separate  into  metal  and  cyanogen.  If  the  cyanide  is  heated 


112 

in  a  narrow  glass  tube,  the  escaping  cyanogen  may  be  ignited, 
burning  with  a  pinkish-lavender  flame.  The  gas  is  also  rec- 
ognizable by  its  odor  of  bitter  almonds.  Mercuric  cyanide 
may  be  decomposed  by  dissolving  in  water  and  passing  hy- 
drogen sulphide  through  the  solution ;  mercuric  sulphide  is 
precipitated  and  hydrocyanic  acid  enters  into  solution. 

The  insoluble  compounds  of  ferrocyanogen  and  ferricy- 
anogen  are  decomposed  by  boiling  with  sodium  carbonate  or 
sodium  hydroxide;  sodium  ferrocyanide  and  ferricyanide 
respectively  are  formed,  together  with  an  insoluble  carbonate 
or  an  oxide  of  the  metal : 

Pb2Fe(CN)6  +  2X0,00,  =  Na4Fe(CN)6  +  2PbCO3 ; 

Cu2Fe(CX)6  +  4XaOH  =  JSa4Fe(CJNT)6  +  2CuO  +  2H2O. 
The  aqueous  solution  is  filtered  and  the  filtrate  tested  for  the 
acid,  while  the  carbonates  or  oxides  are  dissolved  in  dilute 
nitric  acid.  If  sodium  hydroxide  is  employed  as  the  decom- 
posing agent,  lead,  zinc,  and  aluminium,  and  also  arsenic, 
antimony,  and  tin,  may  enter  into  solution.  In  such  cases  a 
portion  of  the  alkaline  solution  is  tested  for  lead,  zinc,  and 
aluminium  by  saturating  the  solution  with  hydrogen  sul- 
phide, thereby  precipitating  the  first  two  metals  as  sulphides 
and  the  last  as  hydroxide.  The  filtrate  from  any  precipitate 
which  may  have  been  produced,  or  the  clear  solution  if  no 
precipitate  was  produced  by  hydrogen  sulphide,  is  acidulated 
with  hydrochloric  acid  to  precipitate  arsenic,  antimony,  and 
tin  as  sulphides. 

If  sodium  hydroxide  is  used  in  decomposing  the  ferri- 
cyanide, sodium  ferricyanide  is  formed,  providing  the  metallic 
oxide  produced  in  the  operation  is  not  further  oxidizable  : 
Cus(Fe(CN)6>2  +  6NaOH  -  2Na3Fe(CN)6  +  3CuO  +  3H2O. 
If,  however,  the  separated  oxide  is  capable  of  further  oxida- 
tion, this  oxidation  takes  place,  accompanied  by  the  reduction 
of  the  sodium  ferricyanide  to  sodium  ferrocyanide : 


113 

Fe3(Fe(CN)6)2  +  SNaOH  =  2Na3Fe(CN)6  +  3Fe(OH)2  + 

2NaOH  ; 
2Na3Fe(CN)6  +  3Fe(OH)2  +  2NaOH  =±  2Na4Fe(CN)6  + 

Fe2(OH)6  +  Fe(OH)2. 

Consequently,  in  such  cases  to  detect  the  acid  the  substance 
is  fused,  whenever  possible,  with  sodium  carbonate. 

To  detect  alkalies  in  ferrocyanogen  and  ferricyanogen  com- 
pounds, the  latter  are  decomposed  into  sulphates,  carbon 
monoxide,  and  ammonium  sulphate,  by  being  heated  with 
concentrated  sulphuric  acid  : 

CuK2Fe(CN)6  +  6H2SO4  +  6H2O  =  FeSO,  +  CuSO4  + 
K2SO4  +  6CO  +  3(N.H4)2SO4. 

5.    SILICATES. 

Before  silicates  can  be  analyzed  they  must  be  finely  pul- 
verized (page  104). 

(a)  Silicates  soluble  in  water  or  silicates  that  may  be  decom- 
posed by  acids  are  best  decomposed  by  being  boiled  with  con- 
centrated hydrochloric  acid ;  by  this  procedure  silicic  acid  and 
chlorides  of  the  respective  metals  are  formed  ;  for  example  : 

K2Si03  +  2HC1  =  H2Si03  +  2KC1. 

Boiling  is  continued  until  complete  decomposition  has  taken 
place,  and  no  gritty  particles  are  detected  on  stirring  with  a 
glass  rod.  The  solution  is  then  evaporated  to  the  dryness 
of  dust  on  a  water-bath  (see  1,  page  69),  to  convert  the  solu- 
ble silicic  acid  into  insoluble  amorphous  silicic  acid.  The 
dry  residue  is  then  moistened  with  a  little  concentrated  hydro- 
chloric acid,  to  convert  any  basic  chlorides  (of  Fe,  Al,  Mg, 
etc.)  into  neutral  chlorides,  thereby  rendering  them  soluble ; 
finally  the  chlorides  of  the  bases  are  extracted  with  water  and 
dilute  hydrochloric  acid. 

(b)  Silicates  that  are  not  decomposed  by  acids  must  either 
be  fused  with  a  carbonate  of  an  alkali  or  decomposed  by 

h  10* 


114 

hydrofluoric  acid.  To  determine  which  method  should  be 
employed,  the  silicate  is  tested  for  the  presence  of  an  alkali. 
For  this  purpose  a  small  portion  of  the  powdered  silicate, 
moistened  with  hydrochloric  acid,  is  placed  on  a  platinum  wire 
and  held  in  the  non-luminous  flame  of  a  Bunsen  burner,  to 
observe  whether  a  color  is  imparted  to  the  flame  (sodium, 
yellow ;  potassium,  violet).  If  alkalies  are  absent  the  method 
of  decomposition  by  means  of  sodium  carbonate  is  to  be  em- 
ployed ;  whereas  if  alkalies  are  present,  in  order  to  test  for 
them,  the  silicate  must  be  decomposed  with  hydrofluoric  acid. 

(c)  In  case  the  fusion  is  to  be  made  with  sodium  carbonate 
(preferably  with  sodium  potassium  carbonate),  one  part  of  the 
finely  pulverized  substance  is  thoroughly  mixed  with  six  parts 
of  sodium  potassium  carbonate,  placed  in  a  platinum  cruci- 
ble, and  the  mixture  fused  by  means  of  the  blast-lamp.    The 
silicate  is  decomposed  by  the  carbonate  of  an  alkali,  with  the 
production  of  a  silicate  of  the  alkali  (or  at  least  silicates  that 
are  decomposed  by  acids)  and  a  carbonate  of  the  metal  : 

CaSi03  +  NaKCOs  -  NaKSiO8  +  CaCO3 ; 

CaSi2O5  +  2NaKCO3  =  2NaKSiO8  +  CaCO3  +  CO2. 
On  disintegrating  the  fused  mass  with  hydrochloric  acid,  ac- 
cording to  a,  page  113,  silicic  acid  remains  insoluble,  and  the 
chlorides  of  the  metals  together  with  sodium  chloride  and 
potassium  chloride  enter  into  solution. 

(d)  In  using  hydrofluoric  acid  as  a  solvent  the  finely  pulver- 
ized substance  is  placed  in  a  platinum  crucible,  and  treated  with 
the  pure  acid(1)  until  a  thin  paste  is  formed.     The  mixture  is 
stirred  with  a  platinum  wire  (not  with  a  glass  rod)  and  digested, 
at  a  very  gentle  heat,  until  the  substance  is  completely  dissolved. 
By  this  treatment  the  silicates  are  converted  into  fluosilicates : 

1  The  hydrofluoric  acid  must  be  free  from  alkalies,  and,  when  possible, 
freshly  distilled  in  a  platinum  still. 


115 

CaSiO3  +  6HF  =  CaSiF6  +  3H2O ; 

CaSi  A  +  12HF  =  CaSiF6  +  H2SiF6  +  5H2O. 
When  completely  dissolved  concentrated  sulphuric  acid  is 
added  and  heat  applied,  gently  at  first,  but  afterwards  more 
strongly,  to  drive  off  the  excess  of  acid.  The  sulphuric  acid 
converts  the  fluosilicates  into  sulphates,  while  hydrofluosilicic 
acid  is  evolved : 

CaSiF6  +  H2SO4  =  H2SiF6  +  CaSO4. 

The  residue  of  sulphates  is  dissolved  in  water  and  a  little 
hydrochloric  acid. 

When  this  method  is  employed  to  decompose  silicates  con- 
taining barium,  strontium,  or  calcium^  it  is  necessary — espe- 
cially with  barium  and  strontium, — -to  afterwards  fuse  the 
residue  containing  the  barium,  strontium,  or  calcium  sulphate 
with  a  carbonate  of  an  alkali  (page  106)o 

In  mineral  analyses  it  is  often  of  interest  to  ascertain 
whether  the  minerals  contain,  in  addition  to  the  silicates  not 
decomposable  by  acids,  others  that  may  be  decomposed,  thus 
making  separation  possible=  With  this  in  view,  after  having 
mechanically  separated  the  gangue  and  any  other  impurities 
from  the  mineral  proper,  it  is  finely  pulverized,  treated  with 
hydrochloric  acid,  the  solution  evaporated  to  dryness  as  above 
described  (page  113,  a),  and  the  chlorides  resulting  from  the 
decomposed  silicates  dissolved  in  water,,  The  insoluble  residue, 
which  may  contain  silicic  acid  and  undecomposed  silicates,  is 
boiled  with  sodium  carbonate,  which  dissolves  the  silicic  acid 
derived  from  the  decomposed  silicate.  After  acidulating  the 
sodium  carbonate  solution  with  hydrochloric  acid,  evaporating 
to  dryness,  and  extracting  with  hot  water,  the  silicic  acid  re- 
mains as  a  light,  white  powder.  If  a  residue  remain  after 
boiling  a  second  time  with  sodium  carbonate,  it  is  to  be  con- 
sidered an  undecomposable  silicate,  which  is  to  be  further 
tested  according  to  6,  c,  and  d,  page  114. 


V.  DETECTION  OF  BASES  IN  THE  WET  WAY. 


IF  the  substance  to  be  analyzed  is  a  solid  it  is  to  be  dis- 
solved, as  before  described  (page  104). 

To  test  for  bases  in  organic  substances  the  latter  should  be 
incinerated  and  the  bases  extracted  from  the  ash  by  water  or 
acids.  Organic  acids,  etc.,  interfere  with  a  number  of  the 
reactions  used  in  the  detection  of  bases. 

The  reaction  of  solutions  to  be  examined  should  be  tested 
with  litmus  and  turmeric  paper  to  ascertain  whether  they  are 
neutral,  acid,  or  alkaline.  A  number  of  substances  may  be 
present  in  acid  solutions,  which,  in  neutral  solutions,  may  be 
disregarded ;  for  example,  in  the  third  group,  acid  solutions 
must  be  tested  for  phosphates  and  oxalates,  whereas  if  the  solu- 
tions are  neutral  the  tests  for  these  acids  need  not  be  made. 

Regarding  combinations  that  may  arise  during  the  exam- 
ination of  alkaline  solutions  see  6,  page  120. 


116 


PRECIPITATION  OF  THE  DIFFERENT  GROUPS. 

To  separate  the  bases  into  groups  the  following  group 
reagents  are  employed : 

1.  Hydrochloric  acid. 

2.  Hydrogen  sulphide. 

3.  Ammonium  hydroxide. 

4.  Ammonium  sulphide. 

5.  Ammonium  carbonate. 

By  each  of  these  reagents  a  series  of  bases  called  a  group 
is  precipitated.  Bases  that  are  not  precipitated  by  group 
reagents  are  classed  as  a  sixth  group.  (Table  L,  pages  118 
and  119o)  The  rare  elements  are  not  considered  in  this  plan. 


117 


118 


TABLE   I.— GROUP  PRECIPITATIONS. 


GROUP  I. 

Metals  precipitated  by  Hy- 
drochloric Acid. 


GROUP  II. 

Metals  precipitated  by  Hy- 
drogen Sulphide. 


GROUP  HI. 

Metals  precipitated  by  Am- 
monium Hydroxide. 


as  white,  curdy 
AgCl,  argentic  chloride. 

Mercurous  salts, 

as  white,  pulverulent 
Hg2Cl2,  mercurous  chlo- 
ride. 

Lead, 
as  white 
PbCl2,  plumbic  chloride. 


Lead, 
as  black 
PbS,  plumbic  sulphide. 

Mercuric  salts, 

as  black 
HgS,  mercuric  sulphide. 

Copper, 
as  black 
CuS,  cupric  sulphide. 

Bismuth, 

as  brownish-black 
Bi.>S3,     bismuthous     sul- 
"  phide. 

Stannous  salts, 

as  brownish-black 
SnS,  stannous  sulphide. 

Cadmium, 

as  yellow 

CdS,  cadmium  sulphide. 

Arsenic, 

as  yellow 

arsanious  sulphide 
(mixed  with  sulphur 
if  precipitated  from 
arsenic  acid  solutions). 

Stannic  salts, 

as  yellow 
SnS2,  stannic  sulphide. 

Anlimonious  salts, 

as  orange-red 
SbgSg,    antimonious    sul- 
phide. 

Antimonic  salts, 

as  orange-red 

Sb2S6)  antimonic  sulphide 

(together   with 

and  sulphur). 

Gold, 
as  black 
Au2Ss,  auric  sulphide. 

Platinum, 

as  brownish-black 
PtS2,  platinic  sulphide. 


Iron, 

as  reddish- browu 
Fe2(OH)6)  ferric  hydroxide. 

Chromium, 

as  dirty-green 
Cr2(OH)6,  chromic  hydrox- 
ide. 

Aluminium, 

as  white,  gelatinous 
A12(OH)6,  aluminium    hy- 
droxide. 

In  presence  of  phosphoric 
acid  iron  and  alumin- 
ium respectively  are  pre- 
cipitated as  phosphates, 
—thus : 

Iron, 

as  white 

Fe2(PO4)2)  ferric  phosphate. 

Aluminium, 

as  white 

A12(PO.|)2,  aluminium 
phosphate. 

In  presence  of  phosphoric 
acid  or  oxalic  acid  cal- 
cium, strontium,  and 
barium  are  precipitated 
as  phosphates  or  oxa- 
lates,  as  white 
Ca3(PO4)2,  SrC2O4,  etc. 

Magnesium  in  the  pres- 
ence of  phosphoric  acid 
is  precipitated  in  this 
group 

as  white 

MgNH4PO4.    ammonium 
magnesium  phosphate. 

In  presence  of  iron,  man- 
ganese may  be  precipi- 
tated as 

white,  changing  to  brown, 
Mn(OH)2,   manganous   hy- 
droxide. 


119 


TABLE   I.— GKOUP   PKECIPITATIONS.— Continued. 


GROUP  IV. 

Metals  precipitated  by  Am- 
monium Sulphide. 

GROUP  V. 

Metals  precipitated  by  Am- 
monium Carbonate. 

GROUP  VI. 

For  which  there  is  no  Spe- 
cial Group  Reagent. 

Manganese, 

Barium, 

Magnesium. 

as  light-salmon-colored 
MnS,     manganous      sul- 
phide. 

as  white 
BaCO3,  barium  carbonate. 

Strontium, 

Potassium. 
Sodium. 

Zinc, 
as  white 
ZnS,  zinc  sulphide. 

as  white 
SrCO3,  strontium  carbon- 
ate. 

Lithium. 
Ammonium. 

Nickel, 

Calcium, 

as  black 

as  white 

NiS,  nickelous  sulphide. 

CaCO3,   calcium    carbon- 

ate. 

Cobalt, 

as  black 

CoS,  cobaltous  sulphide. 

— 

120 

If  on  the  addition  of  the  reagent  a  precipitate  is  formed, 
it  is  filtered  off  and  carefully  washed.  The  filtrate  should  be 
tested  to  ascertain  whether  the  precipitation  was  complete, — 
that  is,  whether  no  precipitation  takes  place  on  further  addi- 
tion of  the  reagent.  The  precipitate  must  be  collected  only 
on  properly-cut  filters  which  fit  closely  to  the  inner  surface 
of  the  funnel,  and  the  liquid  in  which  the  precipitate  is  sus- 
pended should  be  poured  into  the  filter  down  a  glass  rod. 
The  precipitates  should  be  thoroughly  washed  before  proceed- 
ing with  the  examination.  This  is  not  only  good  preliminary 
practice  for  quantitative  work,  but  is  absolutely  necessary  to 
obtain  exact  results  in  qualitative  analysis. 

Concentrated  solutions  should  be  diluted  with  water  before 
the  examination  is  commenced.  This  dilution  may  cause 
turbidity,  in  consequence  of  the  formation  of  basic  salts  or 
oxychlorides  of  bismuth,  antimony,  or  mercury.  These,  how- 
ever, may  be  redissolved  by  the  addition  of  a  little  nitric  or 
hydrochloric  acid. 

FIRST    GROUP. 

(a)  Neutral  or  acid  solutions  are  treated  with  a  few  drops 
of  dilute  hydrochloric  acid. 
There  will  be  precipitated  : 

Silver,  as  white,  curdy  AgCl,  argentic  chloride. 
Mercurous  salts,  as  white,  pulverulent  Hg2Cl2,  mercu- 

rous  chloride. 

Lead,  as  white,  crystalline  PbCl2,  plumbic  chloride. 
The  latter  is  incompletely  precipitated,  as  it  is  slightly 
soluble  in  water ;  therefore  a  test  for  it  must  also  be  made  in 
the  second  group.  The  solution  in  which  the  precipitation 
takes  place  must  be  cold,  as  plumbic  chloride  is  easily  soluble 
in  hot  water  and  might  remain  in  solution ;  moreover,  small 
quantities  of  mercurous  salts  might  be  overlooked  in  the 


121 

presence  of  nitric  acid,  as,  when  hydrochloric  acid  and  nitric 
acid  are  both  present  and  the  solution  is  warm,  mercurotis 
chloride  is  transformed  into  soluble  mercuric  chloride. 

Furthermore,  it  should  be  observed  whether  the  precipitate 
redissolves  on  the  addition  of  an  excess  of  the  hydrochloric 
acid.  On  the  addition  of  dilute  hydrochloric  acid,  dilute 
solutions  of  compounds  of  bismuth  yield  a  white  precipitate 
of  BiOCl,  bismuth  oxychloride,  which  on  the  further  addition 
of  hydrochloric  acid  is  redissolved  as  BiCl3,  bismuthous  chlo- 
ride. Compounds  of  antimony,  especially  K(SbO)C4H4O6, 
potassium  antimonious  tartrate,  with  dilute  hydrochloric 
acid  form  SbOCl,  antimonious  oxychloride,  which  is  soluble 
in  an  excess  of  the  acid  as  SbCl3,  antimonious  chloride. 
KHC4H4O6,  acid  potassium  tartrate,  if  it  should  have  sepa- 
rated, would  be  redissolved  on  the  further  addition  of  hydro- 
chloric acid : 

KHC4H406  +  HC1  =  H2C4H406  -fKCl. 

Furthermore,  there  may  be  precipitated  in  the  first  group : 
boric  acid  (crystalline),  organic  acids,  and  sulphur.  (Sulphur 
separates  from  hyposulphites  and  polysulphides ; 

Na2S203  +  2HC1  =  2NaCl  +  S  -f-  SO2  +  H2O ; 
(NH4)2S3  +  2HC1  =  2NH4C1  +  S2  +  H2S. 
In  the  first  case  sulphurous  anhydride,  in  the  latter  case  hy- 
drogen sulphide,  is  evolved  with  the  sulphur.     Polysulphides 
are  always  alkaline  in  reaction.) 

Attention  should  be  paid  to  any  gases  evolved  on  treat- 
ment with  hydrochloric  acid  (with  reference  to  the  manner 
of  distinguishing  them  see  pages  99  to  102  and  105).  Sul- 
phurous anhydride  must  be  driven  off  by  heating ;  other- 
wise, on  the  addition  of  hydrogen  sulphide,  separation  of 
sulphur  would  occur  (together  with  the  formation  of  pen- 
tathionic  acid) : 

5S02  +  5H2S  =  H2S506  +  S5  +  4H2O. 
P  11 


122 

Chlorine,  nitrogen  dioxide,  etc.,  should  also  be  expelled  by 
heating  the  liquid. 

(6)  Alkaline  solutions  should  be  treated  with  hydrochloric 
acid  until  acid  in  reaction,  and  any  formation  of  precipitates 
or  evolution  of  gases  observed.  From  alkaline  solutions 
there  may  be  separated  : 

1.  Sulphur  and  sulphides  of  the  metals,  accompanied  by 
the  evolution  of  hydrogen  sulphide. 

The  sulphides  are  the  following  sulpho-acids  :  As2S3,  As2S5, 
Sb2S3,  Sb2S5,  SnS2 :  they  should  be  tested  according  to  the 
directions  given  in  the  chapter  treating  of  them  under  the 
second  group  (see  B,  page  135).  Under  certain  conditions 
CuS,  HgS,  and  NiS  might  also  be  encountered  at  this  stage. 
The  filtrate  from  the  sulphur  or  the  sulphides  which  have 
separated  may  be  examined  directly  for  the  metals  of  the 
fifth  and  sixth  groups. 

2.  Cyanides  of  the  heavy  metals  (which  were  dissolved  in 
cyanides  of  the  alkalies),  with  the  evolution  of  hydrocyanic 
acid.     Concentrated  hydrochloric  acid  is  added  to  the  liquid 
containing  the  precipitate  and  the  whole  heated.     The  cyanides 
are  thereby  converted  into  chlorides,  which  finally  dissolve, 
argentic  chloride  alone  remaining  undissolved.     The  solution 
is  then  examined  for  the  presence  of  metals  of  the  second, 
third,  and  subsequent  groups ;  argentic  chloride  in  the  residue 
is  confirmed  by  testing  its  solubility  in  ammonium  hydroxide. 

3.  Silicic  acid :   gelatinous ;   should  be  confirmed   in   the 
bead  of  microcosmic  salt  (see  4,  page  70).     The  solution, 
together  with  the  precipitate,  is  treated  with  an  excess  of 
hydrochloric  acid,  and  evaporated  to  dryness  on  the  water- 
bath  to  render  the   silicic   acid   insoluble.     The   residue   is 
extracted  with   water   and  a  little  hydrochloric   acid  (page 
113,  a),  and  the  filtrate   examined  for  bases.     It   usually 
contains  nothing  but  the  alkalies. 


123 

4.  Precipitates  of  plumbic  hydroxide,  aluminium  hydrox- 
ide, chromium  hydroxide,  and  zinc  hydroxide  may  be  formed, 
but  on  acidifying  with  hydrochloric  acid  will  immediately 
disappear,  being  converted  into  soluble  chlorides. 

SECOND  GROUP. 

Hydrogen  sulphide  is  conducted  into  the  acid  nitrate  ob- 
tained from  the  precipitate  of  the  first  group,  or  into  the 
solution  in  which  hydrochloric  acid  failed  to  produce  a  pre- 
cipitate, until  a  distinct  odor  of  the  gas  is  observable  in  the 
liquid. 

There  will  be  precipitated  : 

Lead,  as  black  PbS,  plumbic  sulphide. 

Mercuric  salts,  as  black  HgS,  mercuric  sulphide. 

Copper,  as  black  CuS,  cupric  sulphide. 

Bismuth,  as  brownish-black  Bi2S3,  bismuthous  sulphide. 

Gold,  as  black  Au2S3,  auric  sulphide. 

Platinum,  as  brownish-black  PtS2,  platinic  sulphide. 

Cadmium,  as  yellow  CdS,  cadmium  sulphide. 

Arsenious  compounds,  as  yellow  As2S3,  arsenious  sulphide. 

Arsenic  compounds,  as  yellow  As2S3,  arsenious  sulphide 

(with  sulphur). 
Antimonious  compounds,  as  orange-red  Sb2S3,  antimoni- 

ous  sulphide. 
Antimonic   compounds,  as   orange-red   Sb2S5,  antimonic 

sulphide  (together  with  Sb2S3  and  S). 
Stannous  compounds,  as  brownish-black  SnS,  stannous 

sulphide. 

Stannic  compounds,  as  yellow  SnS2,  stannic  sulphide. 
From  solutions  containing  hydrochloric  acid,  when  hydro- 
gen sulphide  is  not  present  in  sufficient  quantity,  lead  is  pre- 
cipitated as  red  Pb2SCl2,  plumbic  sulphochloride,  which  is 


124 

converted  by  further  addition  of  hydrogen  sulphide  into 
black  PbS.  In  solutions  of  mercuric  salts  white  precipitates 
of  double  salts  (for  example,  Hg3S3Cl2)  are  formed,  which  on 
continuing  the  addition  of  hydrogen  sulphide  become  yellow, 
then  brown,  and  finally  are  converted  into  black  HgS. 
Arsenious  acid  is  precipitated  at  once,  arsenic  acid  gradually  ; 
the  precipitation  is  accelerated,  however,  by  heating  (see  1, 
page  26). 

Sulphur  may  also  separate  when  hydrogen  sulphide  is 
introduced  into  the  solution.  This  separation  may  be  caused 
by: 

1.  Chlorine,  bromine,  iodine,  nitrous  acid,  nitrogen  dioxide, 
etc.  (in  consequence  of  their  oxidizing  action  upon  hydrogen 
sulphide)  ;  for  example  : 


N203  -f  H2S  =  2M)  +  H20  +  S. 

On  passing  hydrogen  sulphide  into  solutions  containing  an 
excess  of  nitric  acid  or  nitro-hydrochloric  acid,  sulphur  is 
separated.  The  excess  of  acid  should  be  driven  off  by 
evaporation  and,  after  diluting  with  water,  the  introduction 
of  hydrogen  sulphide  should  be  repeated. 

2.  Sulphurous  acid  (page  121). 

3.  Ferric  salts,  in  consequence  of  their  reduction  to  ferrous 
salts  : 

Fe2Cl6  +  H2S  =  2FeCl2  +  2HC1  -f  S. 
Decolorization  of  the  solution  results  from  the  reduction. 

4.  Chromic  acid  and  chromates,  in  consequence  of  their 
reduction  to  chromic  salts  : 

2H2CrO4  -f-  3H2S  +  6HC1  =  Cr2Cl6  +  8H2O  +  S3. 
The  solution  changes  in  color  from  yellow  to  green.     By 
repeated  introduction  of  hydrogen  sulphide  accompanied  by 
renewed  additions  of  hydrochloric  acid,  the  chromic  acid  is 
completely  decomposed.     If  the  acid  is  not  added  in  sufficient 


125 

quantity,  a  precipitate  is  formed  consisting  either  of  green 
chromic  hydroxide : 

2H2CrO4  +  3H2S  =  Cr2(OH)6  +  S3  +  2H2O, 
or  of  brown  chromium  chromate  : 

3H2Cr04  +  3H2S  =  (CrO)2CrO4  +  S3  +  6H2O. 
5.  Permanganic  acid  and  permanganates,  in  consequence 
of  their  reduction  to  manganous  compounds  : 

2HMnO4  +  5H2S  +  4HC1  —  2MnCl2  +  S5  +  8H2O. 
The  purplish-red  solution  is  decolorized.     The  procedure  is 
the  same  as  in  4,  page  124.     (If  the  hydrochloric  acid  is  not 
added  in  sufficient  quantity,  brown  precipitates  are  formed.) 

THIRD  GROUP. 

From  the  nitrate  of  the  second  group,  or  from  the  solution 
in  which  hydrogen  sulphide  failed  to  produce  a  precipitate, 
the  hydrogen  sulphide  is  expelled  by  boiling.  A  small 
quantity  of  nitric  acid  is  added  and  the  solution  warmed  to 
oxidize  the  bases,  ammonium  chloride  and  afterwards  ammo- 
nium hydroxide  (the  latter  in  not  too  great  excess)  are  added, 
and  the  solution  is  boiled  until  the  odor  of  ammoniacal  gas 
can  no  longer  be  detected. 
There  will  be  precipitated  : 

Iron,  as  reddish-brown  Fe2(OH)6,  ferric  hydroxide. 
Chromium,  as  dirty-green  Cr2(OH)6,  chromic  hydroxide. 
Aluminium,  as  white,  gelatinous  A12(OH)6,  aluminium 

hydroxide. 

In  the  presence  of  phosphoric  or  oxalic  acids, — 
Ferric  phosphate,  Fe2(PO4)2  (white). 
Aluminium  phosphate,  A12(PO4)2  (white). 
Phosphates  and  oxalates  of  col-  1  Ca3(PO4)2,  etc.  (white). 

eium,  strontium,  barium,          )  CaC2O4,  etc.  (white). 
Ammonium  magnesium  phosphate,  MgNH4PO4  (white). 


126 

In  presence  of  iron  some  manganese  may  be  precipitated 
as  Mn(OH)2,  manganous  hydroxide. 

The  hydrogen  sulphide  must  be  expelled,  so  that,  on  the 
addition  of  the  ammonium  hydroxide,  ammonium  sulphide 
may  not  form  and  thereby  precipitate  the  fourth  group  with  the 
third.  '  By  means  of  the  nitric  acid  ferrous  salts  are  converted 
into  ferric  salts ;  in  presence  of  ammonium  chloride  the  fer- 
rous salts  are  not  precipitated,  or  are  precipitated  only  incom- 
pletely. If  the  oxidation  is  not  complete,  a  greenish  precip- 
itate is  obtained  in  the  presence  of  ferrous  salts,  which,  when 
exposed  to  the  air,  oxidizes  and  gradually  changes  to  black 
and  finally  to  reddish-brown  (ferric  hydroxide). 

In  solutions  containing  silicates  the  ammonium  hydrox- 
ide may  precipitate  gelatinous  H2SiO3,  silicic  acid.  H2SO4 
may  possibly  be  formed  (by  the  oxidation  of  the  H2S  passed 
into  the  solution),  and  precipitate  barium  and  strontium  as 
sulphates.  Ammonium  chloride  is  added  to  prevent  the  pre- 
cipitation of  manganese  and  magnesium  (see  3,  page  45,  and 
1,  page  53).  The  ammonium  chloride  should  be  added  in 
excess, — but  not  too  great  excess,  as  thereby  the  precipitation 
of  the  fifth  group  is  unnecessarily  rendered  more  difficult. 
After  the  addition  of  the  ammonium  hydroxide  it  is  neces- 
sary to  boil  the  liquid  until  the  odor  of  ammonia  disappears, 
in  order  to  completely  precipitate  aluminium  and  chromium 
(see  1,  page  41,  and  1,  page  42).  By  this  procedure  the  excess 
of  ammoniacal  gas  is  expelled ;  but  the  boiling  should  not  be 
continued  too  long,  as  the  solution  may  become  acid  (in  con- 
sequence of  the  decomposition  of  NH4C1  with  the  liberation 
of  NH3). 


127 


FOURTH  GROUP. 

To  the  filtrate  from  the  third  group  (to  which  ammonium 
hydroxide  is  again  added),  or  to  the  solution  in  which  am- 
monium chloride  and  ammonium  hydroxide  failed  to  produce 
a  precipitate,  colorless  or  slightly  yellow  ammonium  sulphide 
is  added. 

There  will  be  precipitated  : 

Manganese,   as   light-salmon-colored   MnS,  manganous 

sulphide. 

Zinc,  as  white  ZnS,  zinc  sulphide. 
Nickel,  as  black  NiS,  nickelous  sulphide. 
Cobalt,  as  black  CoS,  cobaltous  sulphide. 
Nickelous  sulphide  is  slightly  soluble  in  an  excess  of  yellow 
ammonium  sulphide,  imparting  a  brown  color  to  the  solution. 
The  nickelous  sulphide  is  completely  separated  on  boiling  the 
solution,  especially  after  the  addition  of  acetic  acid.     Ammo- 
nium sulphide  might  also  precipitate  iron  as  ferrous  sulphide, 
in  case  the  iron  were  held  in  solution  by  organic  substances. 

FIFTH  GROUP. 

From  the  filtrate  of  the  fourth  group,  or  from  the  solution 
in  which  ammonium  sulphide  failed  to  produce  a  precipitate, 
the  ammonium  sulphide  is  expelled  by  boiling,  any  sulphur 
which  may  have  separated  is  filtered  off,  ammonium  hydrox- 
ide and  ammonium  carbonate  are  added  to  the  filtrate,  and 
the  whole  is  boiled  as  long  as  carbon  dioxide  is  evolved. 
There  will  be  precipitated  : 

Barium,  as  white  BaCO3,  barium  carbonate. 
Strontium,  as  white  SrCO3,  strontium  carbonate. 
Calcium,  as  white  CaCO3,  calcium  carbonate. 
On  the  addition  of  commercial  ammonium  carbonate,  acid 
carbonates  soluble  in  water — as,  for  example,  Ca(HCO3)2 — 


128 

are  produced  (page  50),  which,  on  boiling,  are  converted  into 
neutral,  insoluble  carbonates,  with  the  liberation  of  CO2  and 
H2O: 

Ca(HC03)2  -  CaC03  +  CO2  +  H2O. 

The  carbonates  are  soluble  in  an  excess  of  ammonium  chlo- 
ride on  long-continued  boiling  : 

CaC03  +  2NH4C1  =  CaCl2  +  2NH3  +  CO2  +  H2O. 


SIXTH  GROUP. 

In  this  group  are  classed  magnesium,  potassium,  sodium, 
and  lithium.  Ammonium  is  also  classed  with  this  group, 
but  the  test  for  it  must  be  made  in  the  original  substance 
presented  for  analysis. 

(With  reference  to  their  separation  see  Separation  of  the 
Sixth  Group,  page  152.) 

With  this  group  may  also  be  found  the  ferro-  and  ferri- 
cyanides  of  the  alkalies,  cobalticyanides  of  the  alkalies,  etc., 
from  which  the  iron  and  cobalt  are  not  precipitated  by  the 
ordinary  reagents.  Furthermore,  aluminium  may  have  re- 
mained in  solution,  because  of  the  presence  of  organic  sub- 
stances. These  compounds  are  to  be  treated  with  concen- 
trated sulphuric  acid  (page  113)  and  separated  by  the  regular 
group  precipitations. 


SEPARATION  OF  THE   BASES  CONTAINED   IN 
THE  GROUP  PRECIPITATES. 

The  group  precipitates  thus  obtained  are  now  examined 
separately.  The  precipitates  of  the  second  and  fourth  groups 
must  be  examined  immediately,  as  they  oxidize  when  exposed 
to  the  air.  Precipitates  of  the  third  group  must  be  quickly 


129 

filtered,  in  order  to  prevent  the  formation  and  precipitation 

of  manganic  hydroxide ;  for  example  : 

2MnCl2(NH4Cl)2  +  4NH.OH  +  H2O  +  O  =  Mn2(OH)6  + 

8NH4C1. 

If  no  precipitate  is  formed  in  the  third  group,  ammonium 
sulphide  should  be  added  rapidly,  to  prevent  the  separation 
of  manganic  hydroxide.  If  arsenic  or  tin  be  found  in  the 
second  group,  a  portion  of  the  filtrate  is  reserved  for  the  tests 
for  acids  and  the  other  portion  is  used  in  testing  for  bases. 

The  filtrate,  including  the  wash-water,  from  each  group 
precipitation  is  reserved  for  treatment  with  the  succeeding 
group  reagent.  If  no  precipitate  is  produced  by  a  group 
reagent,  it  indicates  that  the  metals  of  that  particular  group 
are  absent.  The  solution  is  then  treated  with  the  succeeding 
group  reagent. 

SEPARATION  OF  THE  FIRST  GROUP. 

The  precipitate  produced  by  hydrochloric  acid,  after  being 
washed  with  cold  water,  is  treated  while  on  the  filter  with 
hot  water ;  any  plumbic  chloride  present  is  dissolved  by  the 
hot  water,  and  may  be  tested  for  in  the  filtrate  by  the  addi- 
tion of  sulphuric  acid,  the  formation  of  a  white  precipitate  of 
PbSOd  indicating  the  presence  of  lead.  Argentic  chloride 
and  mercurous  chloride  would  remain  on  the  filter,  undis- 
solved  by  the  hot  water.  Any  residue  remaining  on  the 
filter  is  washed  with  hot  water  until  free  from  lead  (test 
washings  with  H2SO4),  and  then  treated  with  ammonium 
hydroxide :  mercurous  chloride  is  converted  into  black,  in- 
soluble NH2Hg2Cl,  dimercurous  ammonium  chloride,  while 
argentic  chloride  is  dissolved  as  NH3AgCl,  argent-ammonium 
chloride.  The  ammoniacal  filtrate  is  treated  with  nitric  acid 
until  acid  in  reaction.  A  white  precipitate  of  AgCl  indicates 
the  presence  of  silver. 


130 


TABLE   II.-SEPAKATION   OF   THE   FIEST  GKOUP. 

The  precipitate,  which  may  contain  AgCl,  Hg2Cl2,  PbCl2,  is  treated,  while 
on  the  filter,  with  hot  water : 


Filtrate. 
PbCl2. 

Treat  with  H2SO4 : 
white  precipitate  of  PbSO4  indi- 
cates presence  of  lead. 


Insoluble  Residue. 

AgCl,  Hg2Cl2. 
Treat  with  ammonium  hydroxide  : 


Filtrate. 

Ag 

(as  NH3AgCl). 
Treat  with  HN03 : 
white,   curdy  pre- 
cipitate of  AgCl 
indicates        pres- 
ence of  silver. 


Residue. 
Hg 

as  black 

NH2Hg2Cl  indi- 
cates presence  of 
mercurous  salts. 


To  detect  small  quantities  of  argentic  chloride  in  the  pres- 
ence of  mercurous  chloride,  the  dry  mixture  of  the  chlorides 
is  heated  in  a  small  glass  tube  :  mercurous  chloride  will  vola- 
tilize, while  argentic  chloride  remains  as  a  horny  mass,  which 
may  be  further  tested  on  charcoal  with  the  blowpipe. 

SEPARATION   OF  THE  SECOND  GROUP. 

Of  the  sulphides  of  the  second  group  some  are  basic  and 
others  acid  in  character ;  therefore  some  of  them  are  unacted 
upon  by  ammonium  sulphide,  while  others  are  dissolved  as 
sulpho-salts. 

Soluble. 

Arsenious  sulphide. 

Antimonious  sulphide. 

Antimonic  sulphide. 

Stannous  sulphide. 

Stannic  sulphide. 

Auric  sulphide. 

Platinic  sulphide. 


Insoluble. 
Lead  sulphide. 
Mercuric  sulphide. 
Cupric  sulphide. 
Bismuthous  sulphide. 
Cadmium  sulphide. 


131 

Cupric  sulphide  is  slightly  soluble  in  ammonium  sulphide, 
insoluble,  however,  in  sodium  sulphide  and  in  potassium  sul- 
phide. Mercuric  sulphide  is  insoluble  in  ammonium  sulphide, 
but  soluble  in  sodium  sulphide  and  in  potassium  sulphide 
containing  free  alkali.  Stannous  sulphide  is  insoluble  in 
colorless  ammonium  sulphide,  but  easily  soluble  in  yellow 
ammonium  sulphide. 

To  ascertain  whether  sulphides  of  both  basic  and  acid 
divisions  or  of  only  one  division  are  present,  the  precipitate 
produced  by  hydrogen  sulphide  is  examined  regarding  its  be- 
havior with  ammonium  sulphide.  For  this  purpose  a  small 
portion  of  the  precipitate  in  a  test-tube  is  treated  with  ammo- 
nium hydroxide  and  then  with  yellow  ammonium  sulphide 
and  gently  warmed,  any  residue  remaining  undissolved  is  fil- 
tered off,  and  the  filtrate  is  acidified  with  dilute  hydrochloric 
acid,  to  ascertain  whether  a  sulpho-salt  is  present  in  the  solu- 
tion,— that  is,  whether  a  (colored)  precipitate  of  sulphide  is 
formed. 

If  none  of  the  sulphides  have  gone  into  solution,  and  only 
a  milkiness,  due  to  the  separation  of  sulphur  from  the  yellow 
ammonium  sulphide,  is  produced  on  the  addition  of  the 
hydrochloric  acid,  basic  sulphides  only  are  present,  and  the 
remainder  of  the  precipitate  should  be  treated  according  to 
directions  given  under  A,  page  132. 

If  the  precipitate  is  completely  dissolved,  acid  sulphides 
only  are  present,  and  the  remainder  of  the  precipitate  should 
be  examined  according  to  B,  page  132. 

If  a  portion  of  the  precipitate  remain  undissolved  and 
another  portion  enter  into  solution,  the  entire  remainder  of 
the  precipitate  is  treated  with  ammonium  hydroxide  and  am- 
monium sulphide,  the  insoluble  part  filtered  off  and  examined 
according  to  A,  while  the  solution  (filtrate)  is  treated  accord- 
ing to  B.  (See  Table  III  a,  page  132.) 


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134 

A.    FURTHER  SEPARATION   OF   THE   BASIC   SULPHIDES. 

The  thoroughly  washed  precipitate  of  the  basic  sulphides 
is  taken  from  the  filter,  placed  in  a  porcelain  dish,  and  boiled 
with  dilute  nitric  acid  (adding  fresh  portions  of  water  to  re- 
place that  lost  by  evaporation)  until  no  further  change  takes 
place  in  the  precipitate.  Lead,  bismuth,  copper,  and  cad- 
mium enter  into  solution ;  mercuric  sulphide  remains  insolu- 
ble as  a  heavy  black  powder.  The  mercuric  sulphide  is 
collected  on  a  filter,  washed,  and  then  dissolved  in  nitro- 
hydrochloric  acid,  which  converts  it  into  HgCl2.  After 
evaporating  the  excess  of  acid  and  diluting  with  water,  this 
solution  yields  with  stannous  chloride  a  white  precipitate  of 
Hg2Cl2  or  a  gray  precipitate  of  metallic  mercury. 

If  the  precipitate  of  sulphides  is  completely  dissolved  by 
the  dilute  nitric  acid  (with  the  exception  of  sulphur,  which 
floats  on  the  surface  of  the  liquid),  mercury  was  not  pres- 
ent. White  PbSO4  (see  4  and  6,  page  14)  as  well  as  white 
Hg3S2(NO3)2  (see  4,  page  12)  may  be  precipitated  with  the 
mercuric  sulphide. 

The  excess  of  acid  is  evaporated  from  the  nitric  acid  solu- 
tion obtained  as  above  described,  the  solution  diluted  with  a 
small  quantity  of  water,  and  then  treated  with  dilute  sulphuric 
acid :  lead  is  precipitated  as  white  plumbic  sulphate.  The 
plumbic  sulphate  is  filtered  off,  and  the  filtrate  treated  with 
ammonium  hydroxide.  If  bismuth  is  present  a  white  pre- 
cipitate of  BiO— OH,  bismuth  hydroxide,  insoluble  in  an  ex- 
cess of  the  reagent,  is  produced.  As  a  confirmatory  test  the 
precipitate  should  be  collected  on  a  filter  and  dissolved  in 
dilute  hydrochloric  acid ;  if,  on  adding  the  solution  to  a  large 
quantity  of  water,  a  separation  of  white  bismuth  oxychloride 
takes  place,  the  presence  of  bismuth  is  fully  established. 
Copper  and  cadmium  are  also  precipitated  by  ammonium 
hydroxide,  but  redissolve  in  an  excess  of  the  reagent.  If  the 


135 

solution  is  colored  blue,  copper  is  present.  To  test  for  cad- 
mium the  solution  is  decolorized  by  potassium  cyanide,  and 
hydrogen  sulphide  conducted  into  the  liquid ;  a  yellow  pre- 
cipitate of  CdS  indicates  the  presence  of  cadmium.  If  the 
ammoniacal  solution  is  colorless,  it  is  treated  directly  with 
hydrogen  sulphide  to  ascertain  whether  a  precipitate  of 
yellow  cadmium  sulphide  is  produced. 

(As  plumbic  sulphate  is  soluble  in  concentrated  nitric  acid 
and  also  in  salts  of  ammonium,  it  might  be  overlooked  in  the 
presence  of  an  excess  of  nitric  acid  or  in  consequence  of  the 
incomplete  elimination  of  ammonium  sulphide  (before  dis- 
solving in  nitric  acid),  and  thus  interfere  with  the  tests  for 
other  substances.  At  the  point  where  bismuth  is  precipitated 
by  ammonium  hydroxide,  ferric  hydroxide,  aluminium  hy- 
droxide, etc.,  may  also  be  precipitated,  especially  if  the  original 
precipitate  produced  by  hydrogen  sulphide  has  not  been  suffi- 
ciently washed.  With  copper  may  be  found  nickel  and 
cobalt ;  with  cadmium,  zinc.  Plumbic  hydroxide  might  also 
be  precipitated  here  by  ammonium  hydroxide.) 

B.    FURTHER   SEPARATION   OF   ACID   SULPHIDES. 

The  ammonium  sulphide  solution  may  contain  the  sulpho- 
salts  (NH4)sAsS4,  (NH4)3SbS4,  (NH4)2SnS3,  and  may  yield  on 
the  addition  of  hydrochloric  acid  a  yellow  or  orange-red  pre- 
cipitate of  As2S5,  Sb2S5,  SnS2.  If  only  a  milkiness  or  a  white 
precipitate,  due  to  the  separation  of  sulphur  from  the  am- 
monium sulphide,  is  produced,  it  indicates  the  absence  of  sul- 
phides of  arsenic,  antimony,  and  tin.  (Any  black  SnS  which 
may  have  been  present  originally  would  be  precipitated  here 
as  yellow  SnS2 ;  see  1,  page  33.)  The  colored  precipitate  is 
collected  on  a  filter  and  thoroughly  washed.  The  separation 
of  the  three  sulphides  may  be  accomplished  by  either  of  two 
methods, — by  hydrochloric  acid  or  by  ammonium  carbonate. 


136 

The  separation  by  ammonium  carbonate  is  preferable  in  case 
the  preliminary  examination  indicates  the  presence  of  arsenic. 

1.  Separation  by  Hydrochloric  Acid. — The  precipitate  of 
sulphides,  obtained  by  the  addition  of  hydrochloric  acid  to 
the  ammonium  sulphide  solution  (after  being  pressed  between 
sheets  of  filter  paper  to  remove  the  excess  of  moisture),  is 
treated  with  concentrated  hydrochloric  acid  and  warmed : 
antimony  and  tin  enter  into  solution  as  chlorides,  while 
arsenic  sulphide  and  sulphur  remain  undissolved.  (Cupric 
sulphide  would  also  be  dissolved  by  the  hydrochloric  acid. 
A  test  for  it  may  be  made  by  treating  a  few  drops  of  the 
solution  with  ammonium  hydroxide ;  the  production  of  a 
blue  coloration  indicates  the  presence  of  copper.) 

To  test  for  antimony,  a  few  drops  of  the  hydrochloric  acid 
solution  are  placed  on  platinum  foil  and  a  small  piece  of  zinc 
is  placed  in  the  liquid.  If  antimony  is  present,  a  black  de- 
posit of  metallic  antimony  is  formed  which  adheres  to  the 
platinum  foil.  To  test  for  tin  which  may  be  present  as 
stannic  chloride,  a  fragment  of  metallic  zinc  is  placed  in  the 
remainder  of  the  hydrochloric  acid  solution ;  if  both  tin  and 
antimony  are  present,  they  are  precipitated  as  a  spongy 
metallic  mass.  When  the  precipitation  is  complete,  the  super- 
natant liquid  containing  zinc  chloride  is  poured  off  and  the 
metallic  powder  remaining  is  treated  with  moderately  concen- 
trated hydrochloric  acid,  which  dissolves  the  tin  as  stannous 
chloride,  leaving  the  antimony  undissolved.  The  antimony 
is  removed  by  filtration,  and  the  solution  of  stannous  chloride 
thus  obtained  yields  with  mercuric  chloride  a  precipitate  of 
either  white  mercurous  chloride  or  of  gray  metallic  mercury 
(see  4,  page  33).  On  dissolving  the  sulphides  in  hydrochloric 
acid,  arsenic  sulphide  (together  with  sulphur)  remains  undis- 
solved. To  confirm  the  presence  of  arsenic,  the  arsenic  sul- 
phide is  dissolved  in  warm  concentrated  nitric  acid,  the  solu- 


137 

tion  evaporated  to  dry  ness  on  a  water-bath,  and  the  residue, 
containing  arsenic  acid,  dissolved  in  water.  Ammonium 
chloride,  ammonium  hydroxide,  and  magnesium  sulphate  are 
then  added,  to  ascertain  whether  crystalline  MgNH4AsO4, 
ammonium  magnesium  arseniate,  is  precipitated.  The  precipi- 
tate is  always  crystalline ;  in  very  dilute  solutions  it  forms 
only  after  standing  some  time. 

2.  Separation  by  Ammonium  Carbonate. — If  the  precipi- 
tate is  supposed  to  contain  much  arsenic  sulphide,  it  is  thor- 
oughly washed  with  water  and  then  digested  with  a  concen- 
trated solution  of  ammonium  carbonate.  Arsenic  sulphide 
enters  into  solution  (see  page  22),  while  Sb2S5,  antimonic 
sulphide,  and  SnS2,  stannic  sulphide,  remain  undissolved,  and 
after  being  collected  on  a  filter  and  washed  are  dissolved  in 
,  hydrochloric  acid  and  separated  according  to  1,  page  136. 
The  ammonium  carbonate  solution  of  arsenic  sulphide  is 
evaporated  to  dryness  on  a  water-bath,  and  the  residue  treated 
with  concentrated  nitric  acid  to  oxidize  the  arsenic  to  arsenic 
acid.  The  solution  is  again  evaporated  to  dryness,  dissolved 
in  water,  and  precipitated  with  magnesia  mixture  as 
MgNH4AsO4,  as  described  above.  (To  determine  whether 
the  arsenic,  antimony,  or  tin  existed  in  the  ie  or  ous  condition, 
see  the  pages  treating  of  the  special  reactions  of  these  metals. 
It  is,  of  course,  understood  that,  in  testing  for  arsenic  acid  in 
the  presence  of  phosphoric  acid,  hydrogen  sulphide  is  the  only 
reagent  that  can  be  employed.) 

C.      FURTHER    SEPARATION     OF     ACID     SULPHIDES     IF     THE 
PRESENCE    OF   GOLD    OR   PLATINUM    IS   SUSPECTED. 

The  ammonium  sulphide  solution  may  contain  the  sulpho- 
salts  (NH4)3AsS4,  (NH4)3SbS4,  (NH^SnS,,  (NH4)3AuS3, 
(NH4)2PtS3,  and  may  yield  on  the  addition  of  hydrochloric 
acid  a  yellow,  orange-red,  or  brownish-black  precipitate  of 

12* 


138 

As2S5,  Sb2S5,  SnS2,  Au2S3,  PtS2.  If  only  a  milkiness  or  a  white 
precipitate  is  produced  on  adding  the  hydrochloric  acid  (due 
to  the  separation  of  sulphur  from  the  ammonium  sulphide), 
it  indicates  the  absence  of  sulphides  of  arsenic,  antimony,  tin, 
gold,  and  platinum.  The  colored  precipitate  is  collected  on  a 
filter,  thoroughly  washed,  dried,  and  then  mixed  with  twice 
its  bulk  of  a  dry  mixture  consisting  of  equal  parts  of  sodium 
carbonate  and  potassium  nitrate.  This  mixture  is  introduced, 
in  small  portions  at  a  time,  into  a  porcelain  crucible  contain- 
ing two  parts  (compared  with  the  quantity  of  precipitate)  of 
potassium  nitrate,  which  is  kept  just  at  the  point  of  fusion. 
The  temperature  must  not  be  of  such  a  degree  as  to  decom- 
pose the  potassium  nitrite  resulting  from  the  fusion  of  the 
potassium  nitrate,  as,  when  the  precipitate  is  added,  sodium 
stannate  instead  of  stannic  oxide  may  be  formed.  When  cool, 
the  fused  mass  is  extracted  with  water  containing  alcohol  and 
filtered.  The  alcohol  is  evaporated  from  the  filtrate,  which 
may  contain  arsenic,  and  then  ammonium  hydroxide,  ammo- 
nium chloride,  and  magnesium  sulphate  are  added.  A  white 
crystalline  precipitate  of  ammonium  magnesium  arseniate, 
which  may  appear  immediately  or  after  some  time,  indicates 
the  presence  of  arsenic. 

The  insoluble  residue,  which  may  contain  metallic  gold 
and  platinum,  stannic  oxide,  and  sodium  pyroantimonate,  is 
boiled  with  a  concentrated  solution  of  sodium  hydroxide, 
diluted  with  water,  and  filtered.  The  filtrate,  which  may 
contain  tin  as  sodium  stannate,  is  acidulated  with  hydrochloric 
acid,  concentrated  by  evaporation,  and  a  -piece  of  metallic 
zinc  placed  in  the  solution  to  precipitate  the  tin.  The  pre- 
cipitate is  collected  on  a  filter,  dissolved  in  hydrochloric  acid, 
and  mercuric  chloride  added  to  the  solution.  The  production 
of  a  white  precipitate  of  mercurous  chloride  or  of  gray 
metallic  mercury  indicates  the  presence  of  tin. 


139 

The  residue,  insoluble  in  sodium  hydroxide,  which  may 
contain  gold,  platinum,  and  sodium  pyroantimonate,  is  boiled 
with  concentrated  hydrochloric  acid,  slightly  diluted  with 
water,  and  then  filtered.  A  portion  of  the  filtrate,  which 
may  contain  antimonious  chloride,  is  placed  on  platinum  foil 
and  a  fragment  of  metallic  zinc  placed  in  it.  The  production 
on  the  platinum  of  a  brown  or  black  adherent  coating  indi- 
cates the  presence  of  antimony. 

The  residue  insoluble  in  concentrated  hydrochloric  acid, 
which  may  contain  metallic  gold  and  platinum,  is  dissolved 
by  heating  with  nitro-hydrochloric  acid,  the  solution  evapo- 
rated to  dry  ness  on  a  water-bath,  the  residue  dissolved  in 
water,  and  the  solution  boiled  with  ferrous  sulphate  and  then 
filtered.  The  insoluble  residue  of  gold  on  the  filter  is  fused 
on  charcoal  with  the  blowpipe  to  obtain  the  gold  in  the  form 
of  a  yellow  metallic  globule. 

The  filtrate,  which  may  contain  platinic  chloride,  is  heated, 
and,  while  hot,  hydrogen  sulphide  is  passed  into  the  solution. 
The  precipitate  is  collected  on  a  filter,  dissolved  by  heating 
with  nitro-hydrochloric  acid,  and  evaporated  to  dryness  on  a 
water-bath.  The  residue  is  dissolved  in  a  small  quantity  of 
water,  placed  in  a  wratch-glass,  ammonium  chloride  added, 
and  the  liquid  stirred  with  a  glass  rod.  A  yellow,  crystalline 
precipitate  of  ammonium  platinic  chloride  indicates  the  pres- 
ence of  platinum. 

SEPARATION    OF   THE   THIRD   GROUP. 

The  tests  for  phosphates  and  for  oxalates  need  be  made  in 
this  group  only  when  the  original  substance  was  dissolved  in 
acids  or  when  solutions  having  an  acid  reaction  are  presented 
for  analysis. 

The  precipitate  produced  by  ammonium  hydroxide,  after 
being  washed,  is  warmed  with  just  sufficient  dilute  hydro- 


140 

chloric  acid  to  dissolve  it,  the  solution  cooled,  and  sodium 
hydroxide  added  in  excess.  (To  determine  whether  sodium 
hydroxide  is  present  in  excess,  a -drop  of  the  solution  is  rubbed 
between  the  fingers,  a  slippery  sensation  is  felt  in  case  the 
alkali  is  in  excess ;  the  reaction  with  turmeric  or  litmus  paper 
is  in  this  case  of  no  value,  as  Al2O2(OXa)2  and  Cr2O2(ONa)2, 
which  may  be  formed  here,  are  also  alkaline  in  reaction.) 
Chromium  hydroxide  dissolves  in  the  sodium  hydroxide,  im- 
parting a  green  color  to  the  solution ;  aluminium  hydroxide 
and  aluminium  phosphate  dissolve  without  imparting  a  color ; 
the  remaining  oxides  and  salts  are  precipitated  by  sodium 
hydroxide  in  the  same  manner  as  by  ammonium  hydroxide. 
In  the  presence  of  iron,  chromium  also  may  be  precipitated. 


TABLE   IV.— SEPARATION   OF   THE   THIRD  GROUP,— A. 

The  precipitate,  containing  Fe,  Or,  Al,  Mn,  as  hydroxides, 

Fe,  Al,  Ba.  Sr,  Ca,  Mg,  as  phosphates, 
Ba,  Sr,  Ca  (and  Mg),  as  oxalates, 
is  treated  with  an  excess  of  sodium  hydroxide  and  filtered. 


Filtrate. 

Cr,  Al,  H3P04. 

Cr  :  green  solution  ;  boil  :  a  dirty-green  pre- 
cipitate of  Cr2(OH)6  indicates  the  presence 
of  chromium. 
Al  :  colorless  solution  ;  or  the  filtrate  from  the 
precipitate  of  O2(OH)6  is  divided  into 
two  portions  : 

Precipitate. 

The  remaining  bases  of 
the  group. 
Test     for     phosphoric 
acid  and  oxalic  acid 
according     to    page 
141,  b,  and  then  sep- 
arate  the  bases    ac- 
cording to  Table  V., 
page  142. 

First    portion,  —  treat 
with       ammonium 
chloride  :    a    white 
precipitate             of 
A12(OH)6               or 
A12(PO4)2  indicates 
the  presence  of  Al. 

Second  portion,  —  treat 
with  nitric  acid  and 
ammonium  molyb- 
date  :  a  yellow  pre- 
cipitate      indicates 
the      presence      of 
phosphoric  acid. 

(a)  If  the  sodium  hydroxide  solution  is  emerald-green  in 
color,  it  contains  chromium  as  Cr2O2(ONa)2,  sodium  chromite, 


141 

which  is  precipitated  by  boiling  as  chromium  hydroxide. 
The  filtrate  from  the  chromium  hydroxide  or  the  originally 
colorless  solution  may  contain  aluminium  hydroxide  and 
phosphoric  acid.  A  portion  of  the  solution  is  tested  for 
aluminium  by  the  addition  of  ammonium  chloride :  if  alu- 
minium is  present  a  white,  gelatinous  precipitate  of  aluminium 
hydroxide  or  aluminium  phosphate  (if  phosphoric  acid  is 
present)  is  produced.  Another  portion  of  the  solution  is 
acidulated  with  nitric  acid,  then  gently  warmed,  and  tested 
with  ammonium  molybdate  for  phosphoric  acid.  A  yellow 
precipitate  of  (NH4)3PO4(MoO3)10,  ammonium  phospho- 
molybdate,  indicates  the  presence  of  phosphoric  acid  (see  6, 
page  65). 

(6)  The  precipitate  obtained  on  the  addition  of  sodium 
hydroxide  (in  case  the  original  substance  was  dissolved  in 
acids  or  the  solution  presented  for  analysis  had  an  acid  re- 
action) is  tested  for  phosphoric  and  oxalic  acids.  If  these 
acids  are  absent,  the  precipitate  is  treated  directly  according 
to  IV.,  pages  145  and  146. 

A  small  portion  of  the  precipitate  is  dissolved  in  dilute 
nitric  acid  and  the  solution  divided  into  two  portions.  To 
one  portion  concentrated  nitric  acid  and  ammonium  mo- 
lybdate are  added.  If  phosphoric  acid  is  present,  a  yellow 
precipitate  of  ammonium  phosphomolybdate  will  be  formed, 
either  immediately  or  after  standing  some  time. 

The  second  portion  is  boiled  with  sodium  carbonate,  which 
precipitates  the  bases  as  hydroxides  and  carbonates,  while  the 
oxalic  acid  enters  into  solution  as  sodium  oxalate;  for  ex- 
ample : 

CaC2O4  +  Na2CO3  =  CaCO3  -f  Na2C2O4. 
The  liquid  is  filtered,  and  the  filtrate  acidified  with  acetic 
acid,  then  gently  heated  to  completely  expel  carbon  dioxide, 
and  finally  tested  with  calcium  chloride  for  oxalic  acid.     If 


142 

oxalic  acid  is  present,  a  white  precipitate  of  calcium  oxalate  is 
produced. 

The  remainder  of  the  precipitate  produced  by  the  sodium 
hydroxide  is  now  examined  according  to  I. 
if  both  phosphoric  and  oxalic  acids  are  present ; 

according  to  II. 
if  phosphoric  acid  is  present  and  oxalic  acid  is  absent ; 

according  to  III. 
if  phosphoric  acid  is  absent  and  oxalic  acid  is  present ; 

according  to  IV. 
if  both  phosphoric  and  oxalic  acids  are  absent. 


TABLE   V.— SEPARATION  OF   THE   THIRD  GROUP,— B. 

I.  Separation  if  both  Phosphoric  and  Oxalic  Acids  are  Present. 

Boil  the  nitric  acid  solution  of  the  precipitate  with  tin  foil  to  precipitate 
phosphoric  acid,  filter,  boil  the  filtrate  with  excess  of  Na2CO3,  filter,  dis- 
solve the  precipitate  in  HN03,  add  NH4C1  and  NH4OH  to  the  solution, 
and  filter : 


Precipitate. 

Filtrate. 

Cr,  Fe,  Mn. 

Mn,  Ba,  Sr,  Ca,  Mg 

Fuse  with  Na2CO3  and  KNO3,  ex- 

as nitrates. 

tract  the  mass  with  hot  water  :  a 

Add  (NH4)2S,  and  filter: 

yellow  filtrate  indicates  presence 

of  Cr.     Filter,  dissolve  residue  in 

HC1,   add    NaC2H302,   boil,   and 

Precipitate. 

Filtrate. 

filter  : 

Pale  -  salmon- 

Test  according 

colored 

to  Groups  V. 

Precipitate. 

Filtrate. 

MnS 
indicates   pres- 

(page     148) 
and          VI. 

Brownish-red 

Add(NH4\S: 

ence  of  man- 

(page     152) 

Fe2(OH)4(C2H302)2 
indicates    presence 

pale-salmon- 
colored 

ganese. 
(Compare 

for    Ba,    Sr, 
Ca,  and  Mg. 

of  iron. 

MnS 

Group    IV., 

indicates   pres- 

page 146.) 

ence  of  man- 

ganese. 

143 


II.  Separation  if  Phosphoric  Acid  is  Present  and  Oxalic  Acid  is  Absent. 

Boil  th3  nitric  acid  solution  of  the  precipitate  with  tin  foil  to  precipi- 
tate phosphoric  acid,  filter,  to  the  filtrate  add  NH4C1  and  NH4OH,  filter: 


Precipitate. 

Or,  Fe,  Mn. 
Fuse  with  Na2CO3  and  KNO3,  ex- 
tract the  mass  with  hot  water,  fil- 
ter :    a    yellow    filtrate    indicates 
presence  of  Cr.     Dissolve  residue 
in  HC1,  add  NaC2H302,  boil,  and 
filter  : 

Filtrate. 

Mn,  Ba,  Sr,  Ca,  and  Mg, 

Add  (NH4)2S  and  filter. 

Precipitate. 

Pale  -  salmon- 
colored 
MnS 
indicates   pres- 
ence of  man- 
ganese. 
(Compare 
Group    IV., 
page  146.) 

Filtrate. 

Test  according 
to  Groups  V. 
(page      148) 
and          VI. 
(page      152) 
for    Ba,    Sr, 
Ca,  and  Mg. 

Precipitate. 

Brownish-red 

Fe2(OH)4(C2H302)2 
indicates    presence 
of  iron. 

Filtrate. 

Add  (NH4)2S  : 
pale-salmon- 
colored 
MnS 
indicates   pres- 
ence of  man- 
ganese. 
(Compare 
Group    IV., 
page  146.) 

III.  Separation  if  Phosphoric  Acid  is  Absent  and  Oxalic  Acid  is  Present. 

Boil  the  precipitate,  obtained  by  treatment  with  NaOH,  with  Na2CO3, 
filter,  dissolve  the  precipitate  in  HNO3,  add  NH4C1  and  NH4OH,  filter: 


Precipitate. 

Cr,  Fe,  Mn. 

Fuse  with  Na2CO?  and  KNO3,  ex- 
tract the  mass  with  hot  water,  fil- 
ter :  a  yellow  filtrate  indicates 
presence  of  Cr.  Dissolve  residue 
in  HOI,  add  NaC2H3O2,  boil,  and 
filter : 


Precipitate. 

Brownish-red 
Fe  (OH)4(C2H302)2 
indicates    presence 

of  iron. 


Filtrate. 

Add  (NH4)2S : 

pale-salmon- 
colored 
MnS 

indicates  pres- 
ence of  man- 
ganese. 

(Compare 
Group    IV., 
page  146.) 


Filtrate. 

Test  according  to  Groups  V. 
(page  148)  and  VI.  (page  152) 
for  Ba,  Sr,  Ca,  and  Mg. 


144 


IV.  Separation  if  both  Phosphoric  and  Oxalic  Acids  are  Absent 
Fuse  the  precipitate,  obtained  by  treatment  with  NH4C1  and  NH4OH 
(which  may  contain  Or,  Fe,  and  Mn),  with  Na2CO3  and  KIST03,  extract 
the  mass  with  hot  water,  filter :  a  yellow  nitrate  indicates  presence  of  Cr. 
Dissolve  residue  in  HC1,  add  NaC2H3O2,  boil,  and  filter : 


Precipitate. 

Brownish-red 

Fe2(OH)4(C2H302)2 

indicates  presence  of  iron. 


Filtrate. 


Add 
pale-salmon-colored 

MnS 

indicates  presence  of  manganese. 
(Compare  Group  IV.,  page  146.) 


I.  If  both  phosphoric  acid  and  oxalic  acid  are  present,  the 
remainder  of  the  precipitate  is  dissolved  in  concentrated 
nitric  acid  and  the  solution  heated  with  an  excess  of  tin  foil. 
The  stannic  hydroxide  which  is  produced  precipitates  the 
phosphoric  acid  as  stannic  phosphate : 

3Sn(OH)4  +  4H3PO4  =  Sn3(PO4)4  -f  12H2O. 

The  precipitated  mixture  of  stannic  hydroxide  and  stannic 
phosphate  is  filtered  off,  and  the  residue  repeatedly  washed 
with  hot  water  (to  dissolve  the  nitrates  which  are  soluble  with 
difficulty  in  concentrated  nitric  acid),  and  the  nitrate  is  then 
tested  with  ammonium  molybdate  to  determine  whether  the 
phosphoric  acid  has  been  completely  precipitated.  If  the 
phosphoric  acid  was  not  completely  precipitated,  the  treat- 
ment with  tin  foil  must  be  repeated. 

The  nitrate,  free  from  phosphoric  acid,  is  boiled  with  an 
excess  of  sodium  carbonate;  oxalic  acid  enters  into  solution, 
while  the  bases  are  precipitated  as  hydroxides  and  carbonates. 
This  precipitate  is  collected  on  a  filter  and  then  dissolved  in 
nitric  acid,  and  the  solution  treated  with  ammonium  chloride 
and  ammonium  hydroxide.  Phosphoric  acid  and  oxalic  acid 
having  been  removed,  only  iron,  chromium,  and  manganese 
are  precipitated  (as  hydroxides),  and  are  to  be  separated  ac- 


145 

cording  to  Table  IV.,  page  140.  The  filtrate(1)  from  any 
precipitate  that  may  have  formed  is  to  be  tested  according  to 
Groups  IV.,  V.,  and  VI.,  for  manganese,  barium,  strontium, 
calcium,  and  magnesium. 

II.  If  phosphoric  acid  is  present  and  oxalic  acid  is  absent, 
the  phosphoric  acid  is  removed  as  above  described  (I.)  by 
nitric  acid  and  tin,  the  precipitate  is  then  filtered  off,  and  the 
filtrate  treated  with  ammonium  chloride  and  ammonium  hy- 
droxide to  precipitate  iron,  chromium,  and  magnesium.     This 
precipitate  is  collected  on  a  filter,  separated  according  to  Table 
IV.,  page  140,  and  the  filtrate  tested  according  to  Groups  V. 
and  VI.  for  manganese,   barium,   strontium,   calcium,   and 
magnesium. 

III.  If  phosphoric  acid  is  absent  and  oxalic  acid  is  present, 
the  remainder  of  the  precipitate  obtained  by  treatment  with 
sodium  hydroxide  is  boiled  with  sodium  carbonate,  whereby 
the  oxalic  acid  enters  into  solution.     The  residue  containing 
the  bases  is  filtered  off,  thoroughly  washed,  and  dissolved  in 
nitric  acid.     Ammonium  chloride  and  ammonium  hydroxide 
are  then  added  to  precipitate  iron,  chromium,  and  manganese, 
which  are  collected  on  a  filter  and  separated  according  to 
Table  IV.,  page   140.     The  filtrate  is  tested  according  to 
Group  V.  for  barium,  strontium,  and  calcium.(2) 

IV.  The  precipitate,  which  may  contain  chromium,  iron, 
and  manganese,  is  first  examined  for  chromium.     For  this 
purpose  a  small  portion  of  the  precipitate  is  fused  on  plati- 
num foil  with  sodium  carbonate  and  potassium  nitrate,  and 
the  fused  mass  extracted  with  a  small  quantity  of  hot  water. 
If  the  solution  is  yellow  in  color  (due  to  potassium  chromate), 


1  If  the  tin  foil  contain  copper,  the  filtrate  will  be  blue  in  color. 

2  Traces  of  magnesium  may  be  found  here ;  the  nitrate  from  Group  V. 
should  be  tested  for  it  according  to  the  directions  given  under  Group  VI. 

G         k  13 


146 

chromium  is  present.  If  chromium  is  present,  the  remainder 
of  the  precipitate  is  fused  in  a  crucible  with  sodium  carbonate 
aud  potassium  nitrate,  and,  after  cooling,  the  mass  is  treated 
with  water  to  dissolve  the  potassium  chromate.  The  residue, 
which  may  contain  iron  and  manganese  as  oxides,  should  be 
examined  as  follows  :(1) 

To  separate  iron  from  manganese,  the  remainder  of  the 
precipitate  (if  chromium  is  absent)  or  the  residue  (left  after 
extracting  the  potassium  chromate  with  water)  is  dissolved  in 
the  least  possible  quantity  of  hydrochloric  acid,  and  treated 
with  sodium  acetate  until  the  yellow  color  of  the  liquid  (due 
to  Fe2Cl6)  is  changed  to  claret-red  (due  to  Fe2(C2H3O2)6). 
After  the  solution  is  sufficiently  diluted,  it  is  heated  to  boil- 
ing :  iron  is  precipitated  as  Fe2(OH)4(C2H3O2)2,  basic  ferric 
acetate,  which  is  then  filtered  off,  while  the  manganese  re- 
mains in  solution.  The  latter  is  precipitated  in  the  filtrate 
by  ammonium  sulphide  as  pale-salmon-colored  manganous 
sulphide. 

SEPARATION  OF  THE  FOURTH  CROUP. 

After  washing  the  precipitate,  while  on  the  filter,  with 
water  containing  hydrogen  sulphide,  the  filter  is  pierced 
with  a  glass  rod  and  the  precipitate  washed  with  cold  dilute 
hydrochloric  acid  into  a  beaker  placed  below.  Manganous 

1  If  manganese  is  present,  green  potassium  manganate  is  formed  in  the 
fusion ;  on  extracting  the  fused  mass  with  water,  purplish-red  potassium 
permanganate  is  formed,  together  with  insoluble  brown  MnO(OH)2 : 

3K2MnO4  +  3H2O  =  2KMnO4  +  MnO(OH)2  +  4KOH. 
If  the  resulting  solution  is  purplish  red  in  color,  in  order  to  test  for 
chromium  the  remainder  of  the  precipitate  is  dissolved  in  hydrochloric 
acid..  Chlorine  is  driven  off  by  boiling,  ammonium  chloride  and  am- 
monium hydroxide  are  added  and  the  resulting  precipitate  is  quickly  col- 
lected on  a  filter.  The  precipitate  obtained  will  then  be  sufficiently  free 
from  manganese  to  be  again  tested  for  chromium,  etc.,  as  above  described. 


147 

sulphide  and  zinc  sulphide  are  dissolved  by  the  dilute  hydro- 
chloric acid  as  manganous  chloride  and  zinc  chloride,  while 
nickelous  sulphide  and  cobaltous  sulphide  remain  undissolved. 
The  nickelous  and  cobaltous  sulphides  are  collected  on  a  filter 
and  washed  with  water  containing  hydrogen  sulphide. 


TABLE  VI.— SEPARATION  OF  THE  FOURTH  GROUP. 

The  precipitate,  which  may  contain  MnS,  ZnS,  NiS,  CoS,  is  treated 
with  cold  dilute  hydrochloric  acid  and  filtered : 


Insol.  Residue. 

Filtrate. 

NiS,  CoS. 

ZnCl2,  MnCl2. 

Dissolve  in  nitro-hydrochloric  acid, 
evaporate  excess  of  acid,  neutral- 

Heat to  drive  off  H2S,  add  ex- 
cess of  NaOH,  and  filter: 

ize   remainder  with   NaOH,  add 

HC2H3O2    in     excess     and     then 
NaC2H3O2  and  KNO2  : 

Precipitate. 

Filtrate. 

White 

Zn(ONa)2. 

Precipitate. 

Filtrate. 

Mn(OH)2, 
rapidly 

Treat          with 
H2S: 

Yellow  crystalline 
K6Co2(NO2)12 

NiCL. 
Add  NaOH  : 

changing   to 
brown 

white 
ZnS2 

indicates    presence 
of  cobalt. 

pale-apple- 
green 

Mn2(OH)6, 
indicates   pres- 

indicates  pres- 
ence of  zinc. 

Ni(OH) 

ence  of  man- 

indicates  pres- 

ganese. 

ence            of 

nickel. 

The  hydrochloric  acid  nitrate  is  warmed  until  the  hydrogen 
sulphide  is  completely  driven  off,  and  then  treated  with  sodium 
hydroxide  in  excess.  Manganese  is  precipitated  as  white 
manganous  hydroxide,  which,  when  exposed  to  the  air, 
rapidly  changes  to  brown  manganic  hydroxide ;  while  zinc, 
at  first  precipitated  as  zinc  hydroxide,  is  dissolved  as  Zn(ONa)2, 
sodium  zincate.  The  manganous  hydroxide  is  filtered  off, 
and  the  alkaline  filtrate  treated  with  hydrogen  sulphide, 
which  precipitates  zinc  as  white  zinc  sulphide. 

The  mixture  of  nickelous  sulphide  and  cobaltous  sulphide 


148 

remaining  on  the  filter,  insoluble  in  hydrochloric  acid,  is  dis- 
solved by  heating  with  nitro-hydrochloric  acid.  The  greater 
part  of  the  excess  of  acid  is  driven  off  by  boiling,  and  the 
solution  neutralized  by  adding  sodium  hydroxide  drop  by 
drop  until  a  permanent  precipitate  of  hydroxides  is  formed. 
Acetic  acid  in  excess  and  sodium  acetate  are  then  added,  fol- 
lowed by  the  addition  of  an  excess  of  a  concentrated  solution 
of  potassium  nitrite.  If  cobalt  is  present,  a  yellow  crystal- 
line precipitate  of  potassium  cobaltic  nitrite  is  formed,  either 
immediately  or  after  standing  some  time.  After  several 
hours  the  precipitate  is  filtered  off,  and  the  filtrate  treated 
with  sodium  hydroxide ;  the  formation  of  a  pale-apple-green 
precipitate  of  nickelous  hydroxide  indicates  the  presence  of 
nickel.  (The  precipitate  of  nickel  should  be  tested  in  the 
bead  of  microcosmic  salt ;  see  7,  page  49.) 

SEPARATION    OF    THE    FIFTH    GROUP. 
FIRST   METHOD. 

The  precipitate,  consisting  of  carbonates,  is  dissolved  in 
hydrochloric  acid,  which  converts  the  carbonates  into  chlorides. 
Only  a  small  quantity  of  hydrochloric  acid  is  used,  so  that 
the  solution  may  be  concentrated  but  only  slightly  acid.  A 
small  portion  of  the  solution  of  chlorides  is  treated  with  a 
concentrated  solution  of  calcium  sulphate. 


149 


TABLE  VII.— SEPARATION  OF  THE  FIFTH  GROUP,  FIRST 

METHOD. 

The  precipitate,  which  may  contain  BaC03,  SrCO3,  CaCO3,  is  dissolved 
in  a  small  quantity  of  HC1,  and  a  portion  of  the  solution  treated  with 
CaS04: 


No    precipitate    is 
produced  : 
Ba  and  Sr 
are  absent.     Treat 
the  remainder  of 

A  white  precipitate  is  produced. 
Evaporate  the  remainder  of  the  HC1  solution  to 
dry  ness  on  a  water-bath,  pulverize  the  residue, 
extract  with  strong  alcohol,  and  filter  : 

the  HC1  solution 

with        NH4OH 

Insol,  Residue. 

Filtrate. 

and(NH4)2C204: 

BaCI2. 

SrCl2,  CaCl2. 

white     precipitate, 
CaC204, 
indicates    presence 
of  calcium. 

Place  a  portion 
on  platinum 
wire         and 
hold   in    the 

Evaporate  to  dry  ness  on  a  water- 
bath,  evaporate  residue  twice 
to  dryness  with  cone.  HNO3, 
extract  the  residue  with  strong 

flame  : 

alcohol,  and  filter: 

a    green    color 

imparted    to 
the  flame  in- 

Insol. Residue. 

Filtrate. 

dicates  pres- 
ence of  bar- 

Sr(N03)2. 
Place  a  portion 

Ca(N03)2. 
Evaporate  un- 

ium. 

on  platinum 

til  free  from 

wire         and 

alcohol,   add 

hold    in    the 

NH4OH  and 

flame  : 

(NH4)2C204: 

a  crimson  color 

white    precipi- 

imparted   to 

tate, 

the  flame  in- 

CaC2O4, 

dicates  pres- 

indicates   pres- 

ence of  stron- 

ence of    cal- 

tium. 

cium. 

(a)  If  upon  the  addition  of  the  calcium  sulphate  no  pre- 
cipitate is  formed,  either  immediately  or  after  standing  some 
time,  barium  and  strontium  are  absent.     The  remainder  of 
the  hydrochloric  acid  solution  (to  which  calcium  sulphate  has 
not  been  added)  is  treated  with  ammonium  hydroxide  and 
ammonium  oxalate,  when,  if  calcium  is  present,  a  white  pre- 
cipitate of  calcium  oxalate  is  formed. 

(b)  If  on  the  addition  of  calcium  sulphate  a  white  precipi- 
tate is  immediately  produced,  barium  is  probably  present ;  if 

13* 


150 

a  turbidity  appear  after  some  time,  probably  strontium  only 
is  present.  In  either  case  the  remainder  of  the  hydrochloric 
acid  solution  (which  has  not  been  treated  with  calcium  sul- 
phate) is  evaporated  to  dry  ness  on  a  water-bath ,  and  the 
residue  pulverized  and  extracted  with  strong  alcohol.  Barium 
chloride  remains  undissolved,  while  strontium  chloride  and 
calcium  chloride  enter  into  solution.  The  liquid  is  filtered 
through  a  dry(l)  filter,  and  a  portion  of  the  residue  on  the 
filter  is  placed  on  a  platinum  wire  and  held  in  the  Bunsen 
flame ;  a  green  color  imparted  to  the  flame  indicates  the  pres- 
ence of  barium.  The  alcoholic  filtrate  is  evaporated  on  a 
water-bath  to  ascertain  (by  a  residue  remaining)  whether 
anything  has  entered  into  solution.  Any  residue  (consisting 
of  chlorides)  remaining  is  evaporated  twice  to  dry  ness  with 
an  excess  of  concentrated  nitric  acid  (free  from  chlorine), 
which  converts  the  chlorides  into  nitrates : 

SrCl2  +  2HN03  =  Sr(NO3)2  +  2HC1, 

and  the  residue  of  nitrates  is  then  extracted  with  strong  alco- 
hol as  before  described ;  calcium  nitrate  enters  into  solution, 
while  strontium  nitrate,  which  remains  undissolved,  is  col- 
lected on  a  filter,  and  a  portion  placed  on  a  platinum  wire  and 
held  in  the  Bunsen  flame ;  a  crimson  color  imparted  to  the 
flame  indicates  the  presence  of  strontium.  The  alcoholic  fil- 
trate is  now  evaporated  until  free  from  alcohol,  and  any  traces 
of  strontium  and  barium  are  precipitated  with  a  few  drops 
of  sulphuric  acid,(2)  and  the  liquid  is  filtered  and  tested  for 
calcium  with  ammonium  hydroxide  and  ammonium  oxalate. 
The  formation  of  a  white  precipitate  indicates  the  presence 
of  calcium. 

1  A  filter  which  has  not  been  moistened  with  water. 

2  From  concentrated  solutions  calcium  also  may  be  partly  precipitated, 
although,  because  of  its  solubility,  a  considerable  quantity  of  calcium  sul- 
phate remains  in  solution. 


151 


SECOND    METHOD. 

The  precipitate,  consisting  of  carbonates,  is  dissolved  in  a 
small  quantity  of  acetic  acid,  and  a  small  portion  of  the 
solution  is  tested  for  barium  with  potassium  chromate. 

TABLE   VIIL— SEPAKATION   OF   THE   FIFTH  GKOUP, 
SECOND   METHOD. 


The  precipitate,  which  may  contain  BaCO3,  SrCO3,  CaC03,  is  dissolved 
in  a  small  quantity  of  acetic  acid,  and  a  portion  of  the  solution  treated 
with  potassium  chromate  : 

A  yellow  precipitate  is  produced: 

No  precipitate  is  produced  : 

BaCrO4, 

Ba 

indicating  the  presence  of  barium. 
Treat  the  remainder  of  the  acetic  acid  solu- 

is absent. 
A  portion  of  the  solution  is  tested 

tion  with  potassium  chromate  to  precipi- 
tate  the    barium,   filter,  add   NH4OH  and 

for  Sr  with  CaSO4  : 

(NH4)2CO3  to  the  filtrate,  and  boil  : 

I 

No  precipitate  is 

A  precipitate 

produced  : 

is           pro- 

No     pre- 
cipitate 

A  precipitate  is  produced. 
Collect  the  precipitate  on  a  filter, 

Sr 
is  absent. 

duced  : 

Sr 

is     pro- 

dissolve   the    precipitate    in   a 

Treat  the  remain- 

is present. 

duced  : 
Ca  and  Sr 

small  quantity  of  HC1,  and  test 
a  portion  of  the  solution  for  Sr 

der  of  the  acetic 
acid      solution 

Treat  the  re- 
mainder of 

are       ab- 

withCaS04: 

with       NH4OH 

the     acetic 

sent. 

and  (NH4)2C2O4  : 
white  precipitate, 

acid      solu- 
tion      with 

No  precipitate  is 
produced  : 

Sr 

A  precipitata 
is           pro- 
duced : 

CaC204, 
indicates       pres- 
ence    of     cal- 

H2S04       to 
p  r  e  cipitate 
Sr,        filter, 

is  absent. 

Sr 

cium. 

and        add 

Treat  the  remain- 
der of  the  HC1 

is  present. 
Treat  the  re- 

NH4OH and 

(NH4)2C204 

solution      with 

mainder  of 

to  filtrate  : 

NH4OH        and 

the  HC1  so- 

white precipi- 

(NH4)2C2O4 : 
white  precipitate, 
CaC204, 
indicates       pres- 

lution with 
H2SO4       to 
p  recipitate 
Sr,        filter, 

tate, 
CaC2O4, 
indicates  pres- 
ence of  cal- 

ence    of     cal- 

and       add 

cium. 

cium. 

NH4OHand 

to  filtrate  * 

white  precipi- 

tate, 

CaC2O4, 

indicates  pres- 

ence of  cal- 

cium. 

(a)  If  a  yellow  precipitate  is  formed,  barium  is  present. 
The  barium  is  precipitated  from  the  remainder  of  the  acetic 
acid  solution  by  potassium  chromate.  The  precipitate  is 
filtered  off,  ammonium  hydroxide  and  ammonium  carbonate 


152 

are  added  to  the  filtrate,  and  the  liquid  is  boiled  to  precipitate 
strontium  and  calcium.  If  no  precipitate  is  formed,  strontium 
and  calcium  are  absent;  if  a  precipitate  of  carbonates  is 
formed,  it  is  collected  on  a  filter,  thoroughly  washed,  and 
then  dissolved  in  a  small  quantity  of  hydrochloric  acid. 

The  solution  of  chlorides  produced  by  dissolving  the  car- 
bonates in  hydrochloric  acid  is  divided  into  two  portions,  one 
of  which  is  tested  for  strontium  with  calcium  sulphate.  If 
a  precipitate  is  not  produced  immediately  or  after  standing 
some  time,  strontium  is  absent.  The  other  portion  of  the 
solution  of  chlorides  is  neutralized  with  ammonium  hydroxide 
and  tested  for  calcium  with  ammonium  oxalate.  If,  on  the 
addition  of  calcium  sulphate,  a  precipitate  of  strontium  sul- 
phate is  formed  (thus  showing  the  presence  of  strontium),  the 
second  portion  of  the  solution  of  chlorides  is  treated  with  sul- 
phuric acid,  to  precipitate  the  strontium  as  sulphate,  which  is 
then  filtered  off  and  the  filtrate  tested  for  calcium  with  ammo- 
nium hydroxide  and  ammonium  oxalate. 

(6)  If  no  precipitate  is  formed  on  the  addition  of  potassium 
chromate,  barium  is  absent.  The  remainder  of  the  acetic  acid 
solution  is  then  tested  for  strontium  with  calcium  sulphate 
and  for  calcium  with  ammonium  hydroxide  and  ammonium 
oxalate,  as  described  above  (a). 

SEPARATION    OF   THE   SIXTH    GROUP. 

If  barium  and  -calcium  were  found  in  the  Fifth  Group, 
traces  of  them  may  remain  in  the  filtrate  from  that  group, 
and  must  be  removed  before  proceeding  with  the  separation 
of  the  Sixth  Group.  For  this  purpose  a  few  drops  of  dilute 
sulphuric  acid  are  added  to  the  filtrate  to  precipitate  the 
barium,  and  ammonium  hydroxide  and  ammonium  oxalate 
added  to  precipitate  calcium.  If  precipitates  are  formed, 


153 

they  are  removed  by  filtration.  A  portion  of  the  solution 
thus  rendered  free  from  barium  and  calcium,  or  the  filtrate 
from  the  Fifth  Group  which  originally  contained  no  barium 
or  calcium,  is  tested  for  magnesium  with  ammonium  chloride, 
ammonium  hydroxide,  and  sodium  hydrogen  phosphate.  If 
magnesium  is  present,  a  white,  crystalline  precipitate  of  am- 
monium magnesium  phosphate  will  appear,  either  immediately 
or  after  standing  some  time.  If  magnesium  is  not  present, 
the  remainder  of  the  solution  is  examined  according  to  L, 
page  117;  if  it  is  present,  the  solution  is  to  be  examined 
according  to  II.,  page  118. 

I.  The  remainder  of  the  solution  which  does  not  contain 
magnesium  is  placed  in  a  porcelain  crucible  or  dish  and 
evaporated  to  dryness  on  a  water-bath ;  it  is  then  gently 
heated  over  a  free  flame  until  vapors  of  ammonium  salts 
cease  to  be  evolved.  If  no  residue  remain,  potassium  and 
sodium  are  absent ;  if  a  residue  remain,  it  is  dissolved  in  the 
least  quantity  possible  of  water,  and  the  concentrated  solution 
divided  into  two  portions. 

One  portion  is  placed  in  a  watch-glass,  treated  with  platinic 
chloride  and  a  small  quantity  of  alcohol,  and  stirred  with  a 
glass  rod.  If  potassium  is  present,  a  yellow,  crystalline  pre- 
cipitate of  potassium  platinic  chloride  will  be  formed. 


154 


TABLE    IXrt.—  SEPAKATION   OF   THE   SIXTH   GKOUP. 


A.  Examination  for  Mg,  Kt  Na,  Li. 

Test  the  filtrate  from  the  Fifth  Group  for  traces  of  Ba  with  H2SO4 
and  for  Ca  with  NH4OH  and  (NH4)2C2O4.    If  precipitates  are 
produced,  remove  them   by  filtration.    Test  a  portion  of  the 
solution  free  from  Ba  and  Ca  for  Mg  with  NH4C1,  NH4OH,  and 
Na2HP04  : 

B  .  Examina- 
tion for  Am- 
monium. 

Treat  the 
original 
substance 
or  solution 
with  NaOH 

A  precipitate  is  produced  : 
MgNH4P04, 
indicating  presence  of  magne- 
sium. 

No  precipitate  is  produced. 
Evaporate  the  remainder  of  the 
solution  to  dry  ness  on  a  water- 
bath,  gently  heat  residue  over 

and  boil  : 
the  evolu- 
tion of  am- 
moniacal 

Evaporate  the  remainder  of  the 
solution    to    dryness    on    a 

a  free  flame  until   vapors  of 
ammonium  salts  cease  to  be 

gas,  recog- 
nized by  its 

water-bath,  gently  heat  resi- 
due over  a  free  flame  until 

evolved. 
(If  lithium  has  been  detected 

odor,  etc., 
indicates 

vapors   of   ammonium   salts 
cease  to  be  evolved. 

by  the  flame  test,  proceed  ac- 
cording    to    the    separation 

presence  of 
ammonium. 

Dissolve  residue  in  water  and  a 

under  Table  1X6.) 

few    drops     HC1,    boil,    add 

Ba(OH)o.  filter,  add  (NH4)2CO3 
to  filtrate,  filter,  evaporate  fil- 
trate  to   dryness    on    water- 
bath,  and  gently  heat  residue 
over  a  free  flame  until  vapors 
of  ammonium  salts  cease  to 

A  residue  remains  : 
KC1,  NaCl. 
Dissolve    in    small 
quantity  of  water 
and   divide    into 

A  residue 
does  not 
remain  : 
K  and  Na 
are       ab- 

be evolved. 
(If  lithium  has  been  detected 
by  the  flame  test,  proceed  ac- 
cording   to    the    separation 
under  Table  1X6.) 

two  portions. 
To  one  portion  add 
PtCl4:    a  yellow, 
crystalline      pre- 
cipitate, 

sent. 

(KCl)2PtCl4, 

indicates    presence 

A  residue  remains  : 

A  residue 

of  potassium. 

KC1,  NaCl. 

does  not 

To  the   other   por- 

Dissolve   in    small 
quantity  of  water 

remain  : 
K  and  Na 

tion    add    clear, 
freshly-prepared 

and    di'vide   into 

are       ab- 

solution of  potas- 

two portions. 

sent. 

sium       pyroanti- 

To  one  portion  add 

monate  :  a  white, 

PtCl4:   a  yellow, 

crystalline      pre- 

crystalline    pre- 

cipitate, 

cipitate, 

NasHaSbaOi, 

(KCl)2PtCi4. 

indicates    presence 

indicates    presence 

of  sodium. 

of  potassium. 

To   the  other  por- 

tion   add    clear, 

freshly  -  prepared 

solution  of  potas- 

sium      pyroanti- 

monate  :  a  white, 

crystalline      pre- 

cipitate, 

Na2H2Sb207, 

indicates    presence 

of  sodium. 

155 


TABLE    1X6.— SEPARATION    OF    THE    SIXTH    GROUP    (IN 
THE   PRESENCE   OF   LITHIUM.) 

K,  Na,  Li. 

If  a  residue  remain  (see  Table  IXa.),  moisten  with  cone.  HC1,  evapo- 
rate to  dryness  on  a  water-bath,  extract  residue  with  a  mixture  of  absolute 
alcohol  and  ether,  and  filter: 


Insol.  Residue. 

KC1,  NaCl. 

Divide  into  two  portions. 

To  one  portion  add  PtCLj:  a  yellow  crys- 

talline precipitate, 

(KCl)2PtCl4, 

indicates  presence  of  potassium. 
To  the  other  portion  add  clear,  freshly- 
prepared  solution  of  potassium  pyro- 
antimonate  :  a  white,  crystalline  pre- 
cipitate, 


indicates  presence  of  sodium. 


Filtrate. 

Lid. 

Evaporate  to  dryness  on  a  water-bath. 

Place  a  portion  of  the  residue  on  a 
clean  platinum  wire  and  hold  in  the 
non-luminous  flame :  a  carmine-red 
color  imparted  to  the  flame  indicates 
presence  of  lithium. 


The  second  portion  is  tested  for  sodium  by  adding  a  clear, 
freshly-prepared  solution  of  potassium  pyroantimonate.  So- 
dium salts  yield  with  potassium  pyroantimonate,  either  im- 
mediately or  after  standing  some  time,  a  white,  crystalline 
precipitate  of  sodium  pyroantimonate.  The  solution  to  be 
tested  for  sodium  must  not  be  acid  in  reaction,  or  flocculent 
antimonic  acid  will  be  precipitated.  If  acid  in  reaction,  the 
solution  should  be  exactly  neutralized  with  ammonium  hy- 
droxide before  making  the  test  with  potassium  pyroantimonate. 

To  detect  small  quantities  of  potassium  and  sodium,  ad- 
vantage may  be  taken  of  their  behavior  in  the  non-luminous 
flame.  Sodium  imparts  a  yellow  color,  potassium  a  violet 
color,  to  the  flame.  To  detect  the  potassium  flame  in  the 
presence  of  the  sodium  flame  (as  the  intense  yellow  sodium 
flame  obscures  the  weaker  violet  potassium  flame),  a  piece  of 
blue  glass  (cobalt  glass)  or  an  indigo  prism  (which  absorbs  the 
yellow  rays)  may  be  employed.  Viewed  through  blue  glass 
or  an  indigo  prism  the  potassium  flame  appears  crimson-red 
in  color. 


156 

II.  If  magnesium  is  present  in  the  solution,  it  must  be 
removed  before  the  tests  for  potassium  and  sodium  can  be 
made.     For  this  purpose  the  solution  containing  magnesium 
is  evaporated  to  dryness  on  a  water-bath,  and  the  residue 
gently  heated  over  a  free  flame  until  the  vapors  of  ammonium 
salts  cease  to  be  evolved.     The  residue  is  then  dissolved  in 
water  and  a  few  drops  of  hydrochloric  acid.     (The  presence 
of  ammonium  salts  interferes  with  the  precipitation  of  mag- 
nesium ;  see  1,  page  53.     The  residue  does  not  completely 
dissolve  in  water,  as  part  of  the  magnesium  salts  were  con- 
verted into  insoluble  basic  salts  by  the  heating.) 

The  solution  is  heated  to  the  boiling  point  and  barium 
hydroxide  added,  whereby  magnesium  hydroxide  is  precipi- 
tated : 

MgCl2  +  Ba(OH)2  =  Mg(OH)2  +  BaCl2. 
(Any  sulphuric  acid  which  might  be  present  would  also  be 
precipitated.)  The  magnesium  hydroxide  is  filtered  off,  and 
the  filtrate  treated  with  ammonium  carbonate  to  precipitate 
the  barium  of  the  barium  chloride  as  barium  carbonate.  The 
barium  carbonate  is  filtered  off,  the  filtrate  evaporated  to  dry- 
ness,  and  the  residue  gently  heated  in  a  porcelain  dish  or 
crucible  until  vapors  of  ammonium  salts  cease  to  be  evolved, 
then  dissolved  in  a  small  quantity  of  water  and  the  solution 
divided  into  two  portions  and  tested  for  potassium  and  sodium 
as  described  under  I.,  page  117. 

III.  If  lithium  has  been  detected  by  the  flame  test  in  the 
residue  mentioned  in  Table  IXa.,  the  residue  is  moistened 
with  concentrated  hydrochloric  acid  (which  converts  the  bases 
into  chlorides),  and  evaporated  to  dryness  on  a  water-bath. 
The  residue  remaining  is  extracted  with  a  mixture  consisting 
of  equal  volumes  of  absolute  alcohol  and  ether.     Lithium 
chloride  enters  into  solution,  leaving  potassium  chloride  and 
sodium  chloride  undissolved.     The  liquid  is  filtered,  the  fil- 


157 

trate  evaporated  to  dryness  on  a  water-bath,  and  a  portion  of 
the  residue  placed  on  a  platinum  wire  and  held  in  the  non- 
luminous  flame.  If  lithium  is  present  a  carmine-red  color 
will  be  imparted  to  the  flame. 

The  residue  insoluble  in  alcohol  and  ether  is  dissolved  in  a 
small  quantity  of  water  and  divided  into  two  portions.  One 
portion  is  placed  in  a  watch-glass,  platinic  chloride  and  a 
few  drops  of  alcohol  are  added,  and  the  liquid  is  stirred  with 
a  glass  rod.  If  potassium  is  present  a  yellow,  crystalline  pre- 
cipitate of  potassium  platinic  chloride  will  be  formed.  The 
other  portion  is  placed  in  a  watch-glass  and  treated  with  a 
clear,  freshly-prepared  solution  of  potassium  pyroantimonate 
and  the  liquid  stirred  with  a  glass  rod.  If  sodium  is  present 
a  white,  crystalline  precipitate  of  potassium  pyroantimonate 
will  be  formed. 


To  test  for  the  presence  of  ammonium  salts,  a  portion  of 
the  original  substance  or  solution  presented  for  analysis  is 
placed  in  a  test-tube,  treated  with  a  solution  of  sodium  hy- 
droxide, and  boiled.  If  ammonium  salts  are  present  ammo- 
iiiacal  gas  will  be  evolved,  which  may  be  recognized  by  its 
odor,  by  its  changing  turmeric  paper,  moistened  with  water, 
brown,  and  by  its  forming  white  clouds  of  ammonium  acetate 
when  a  glass  rod  moistened  with  acetic  acid  is  held  in  the 
atmosphere  containing  the  gas. 

In  using  turmeric  paper  in  this  test  care  must  be  taken  that 
the  turmeric  paper  does  not  come  in  contact  with  the  sides 
of  the  test-tube,  as  in  such  case  the  yellow  paper  may  be 
changed  to  brown  by  sodium  hydroxide  which  may  be  on 
the  glass.  Likewise  care  must  be  taken  that  in  the  ebul- 
lition of  the  liquid  none  of  it  is  projected  on  the  turmeric 
paper. 

14 


VI.  EXAMINATION  FOR  ACIDS. 


THE  examination  for  acids  should  always  be  preceded  by 
the  examination  for  bases  and  by  the  preliminary  examination. 
(See  pages  90,  91,  and  succeeding  pages.) 

The  number  of  acids  to  be  taken  into  consideration  depends 
upon  the  number  of  bases  present  and  upon  the  results  of  the 
preliminary  examination.  Acids  which  form  insoluble  com- 
pounds with  the  bases  found  in  the  solution  need  not  be 
sought  for ;  as,  for  example,  if  silver  is  found  in  the  solution, 
hydrochloric  acid  cannot  be  present,  or,  if  barium  is  found, 
it  is  useless  to  look  for  sulphuric  acid.  In  neutral  solutions 
containing  heavy  metals,  only  a  limited  number  of  acids  are 
to  be  considered,  as  most  of  the  salts  of  the  heavy  metals  are 
insoluble  in  water. 

In  solutions  having  an  acid  reaction  all  the  acids  are  to  be 
considered  which,  with  the  bases  present,  form  salts  soluble 
in  acid  solution.  (For  solubilities  see  Properties  of  the  Acids, 
page  59  and  succeeding  pages.) 

If  heavy  metals  are  present  they  must,  in  many  cases,  be 
removed  before  proceeding  with  the  tests  for  acids.  When 
possible,  this  is  accomplished  by  the  addition  of  an  excess  of 
sodium  carbonate  to  the  solution,  thereby  precipitating  the 
metals  as  carbonates  or  oxides.  The  precipitate  is  filtered  off, 
and  the  filtrate  is  divided  into  two  unequal  portions.  The 
larger  portion  is  neutralized  with  nitric  acid,  and  the  smaller 
portion  with  acetic  acid  (to  be  used  in  testing  for  nitric  acid). 
It  is  advisable  to  gently  heat  the  solution  after  acidulation,  in 
158 


159 
• 
order  to  completely  expel  carbon  dioxide.(1)     Stannic  oxide 

and  arsenic  are  removed  by  precipitating  with  hydrogen  sul- 
phide. In  this  operation  sulphuric  acid  may  result  from  the 
oxidation  of  the  hydrogen  sulphide.  In  such  cases  the  origi- 
nal solution  should  be  tested  directly  for  sulphuric  acid  and 
hydrochloric  acid. 

In  the  examination  of  solutions  having  an  alkaline  reaction, 
they  should  be  neutralized  with  nitric  acid  or  acetic  acid.  In 
case  a  precipitate  is  produced  the  acid  should  be  added  in 
excess,  the  precipitate  filtered  off,  and  the  filtrate  neutralized 
with  an  alkali.  (See  page  122,  6.) 

Salts  which  are  insoluble  in  water  are  examined  for  acids 
by  treating  them  directly  (without  first  dissolving  them)  with 
a  solution  of  sodium  carbonate.  When  heated  to  boiling  the 
acid  enters  into  solution  as  a  sodium  salt,  while  the  base 
remains  as  an  insoluble  oxide  or  carbonate.  The  liquid  is 
filtered,  and  the  filtrate  containing  the  sodium  salts  is  neu- 
tralized with  nitric  acid  or  acetic  acid  as  above  described. 

In  examining  for  acids  when  fusion  is  necessary,  see  the 
chapter  on  Solution  and  Fusion,  page  103. 


The  neutral  solution  is  first  examined  regarding  its  be- 
havior with  the  three  group  reagents :  BaCl2,  Pb(C2H3O2)2, 
and  AgM)3. 

The  acids(2-  which  produce  precipitates  with  the  group 
reagents  and  the  properties  of  the  precipitates  are  given  in 
the  following  table. 

1  If  the  carbon  dioxide  has  not  heen  completely  expelled,  precipitates 
of  carbonates  may  be  produced  on  the  addition  of  the  three  group  re- 
agents ;  with  barium  chloride  soluble  barium  bicarbonate  might  be  formed, 
which  would  appear  as  a  precipitate  only  after  boiling. 

2  For  a  classification  of  the  acids  composing  the  four  groups,  see  page 
59  and  the  succeeding  pages ;  in  this  classification  oxalic  acid  and  tartaric 
acid  belong  to  the  second  group,  and  acetic  acid  to  the  fourth  group. 


160 


TABLE   X.— BEHAVIOK   OF   THE   ACIDS 


PRECIPITATE  IN  THE  PRESENCE  OF 

BaCl2. 

Group  I, 
Group  II,    . 

Group  III,  - 
Group  IV,  - 

\  Sulphuric  acid:  .... 

white  (insoluble  in  HC1)    .... 
white  (insoluble  in  HC1)    .... 

white  (soluble  in  HC1  :  with  evo- 
lution of  SO2) 
white  (soluble  in  large  quant,  of 
water  ;    soluble   in   HC1  :    with 
evolution  of  SO,  and  separation 
of  S) 
white  (soluble  in  HC1)           .    .    . 

L  Hydrofluosilicic  acid  :    . 
'  Sulphurous  acid  :    .    <    . 
Hyposulphurous  acid  :  . 

Phosphoric  acid  :    .    .-*.', 
Boric  acid  ;      

white  (precipitated  only  in  cone, 
solutions  ;  soluble  in  HC1) 

white  (soluble  in  HC1)   
white  (soluble  in  HC1  :  with  effer- 
vescence) 
white  (soluble  in  HC1)           .    .    . 

Hydrofluoric  add:     .    . 
Carbonic  acid:    .... 

Silicic  acid:     
Arsenious  acid:  .... 
Arsenic  acid  :      .... 
Chromic  acid:     .... 
Oxalic  acid:    

white  (soluble  in  HC1) 

white  (soluble  in  HC1)   
yellow  (soluble  in  HC1)      .... 
white  (soluble  in  HC1)   

white  (soluble  in  HC1)   

Hydroferrocyanic  acid  : 
Hydroferricyanic  acid: 

161 


WITH  THE   GKOUP   KEAGENTS. 


Pb(C2H302)2. 

AgNO3. 

white  (insoluble  in  HNO  ) 

white  (soluble  in  HNO3)     .    . 

white    (soluble   in    HNO3;    with 
separation  of  S) 

white  (soluble  in  HNO3)     .... 

white    (soluble    in    excess   of   re- 
agent ;  soluble  in  HNO3) 

white  (soluble  in  HNO3) 

white  (soluble  in  HNO3  ;   becomes 
gray  on  boiling) 
white   (soluble   in   HNO3;    rapidly 
becomes  black) 

yellow  (soluble  in  HNO3) 
white  (precipitated  only  from  cone, 
solutions  ;  soluble  in  HNO3  ;  de- 
composed by  water) 

white    (soluble    in    HN03  ;    with 
effervescence) 
white  (soluble  in  HNO3)     .... 
white  (soluble  in  HNO3)     .... 
white  (soluble  in  HNO3)     .    .    .    . 
yellow  (soluble  in  HNO3)   .... 
white  (soluble  in  HNO3)     .... 
white  (soluble  in  HNO3)     .... 

white    (crystalline,  soluble  in  hot 
water) 
white  (soluble  with  great  difficulty 
in  water) 
yellow  (crystalline,  soluble  in  hot 
water) 
white  (insoluble  in  water  ;  soluble 
in  HNO3) 
white  (insoluble  in  HNO3)      .    .    . 

white  (soluble  in  HNO3  ;  on  boiling 
becomes  yellow  or  brown) 
yellow  (soluble  in  HNO3) 
yellow  (soluble  in  HNO3) 
reddish  brown  (soluble  in  HN03) 
purplish  red  (soluble  in  HNO3) 
white  (soluble  in  HNO3) 
white  (soluble  in  HNO3  ;  separation 
of  Ag  on  boiling) 

white  (curdy,  insoluble  in  HNO3) 
yellowish  white  (insoluble  in  HNO3) 
yellow  (insoluble  in  HNO3) 
white  (curdy,  insoluble  in  HNO3) 

white  (insoluble  in  HNO3) 
yellow  (insoluble  in  HN03) 

black  (soluble  in  HNO3  011  warm- 
ing) 
yellow  coloration       

white  (becomes  brown,  due  to  sep- 
aration of  PbO  ) 

black  (soluble  in  HNO5  on  warm- 
ing) 
white    (soluble   in   large   quant,    of 
water) 
white  (=AgCl) 

162 

In  many  cases  reasonably  certain  conclusions  as  to  which 
acids  are  present  may  be  drawn  from  the  color  of  the  pre- 
cipitates and  from  the  behavior  of  the  latter  with  the  different 
solvents,  if  at  the  same  time  it  is  considered  which  acids  could 
possibly  be  present  under  the  existing  conditions ;  for  ex- 
ample, if  a  precipitate  soluble  in  nitric  acid  is  produced  by 
argentic  nitrate,  the  presence  of  hydrochloric  acid,  hydro- 
bromic  acid,  etc.,  is  excluded.  If  the  precipitate  produced 
by  barium  chloride  is  insoluble  in  acids,  sulphuric  acid  or 
hydrofluosilicic  acid  must  be  present. 

The  presence  of  the  different  acids,  however,  is  to  be 
further  established  as  follows  : 

Sulphuric  Acid.     (Sulphates.) 

Sulphates  when  fused  (as  in  the  preliminary  examination) 
with  sodium  carbonate  on  charcoal  and  a  portion  of  the  fused 
mass  is  placed  on  a  silver  coin  and  moistened  with  water  pro- 
duce a  brownish  or  black  stain  on  the  coin. 

Barium  chloride  produces  a  white  precipitate  of  barium 
sulphate,  insoluble  in  acids. 

Plumbic  acetate  produces  a  white  precipitate  of  plumbic 
sulphate,  soluble  in  neutral  ammonium  tartrate. 

Tests  for  sulphuric  acid  should  never  be  made  in  solutions 
which  have  been  treated  with  hydrogen  sulphide,  because  of 
the  probability  of  the  presence  of  sulphuric  acid  resulting 
from  the  oxidation  of  hydrogen  sulphide. 

Tests  for  sulphuric  acid  can  be  made  in  acid  solutions  con- 
taining bases. 

Hydrofluosilicic  Acid.     (Silicofluorides.) 

Hydrofluosilicic  acid  is  not  precipitated  by  plumbic  acetate, 
but  is  precipitated  by  potassium  nitrate  as  gelatinous  potas- 
sium silicofluoride  (see  3,  page  60). 


163 

Sulphurous  Acid.     (Sulphites.) 

Sulphites  when  fused  with  sodium  carbonate  on  charcoal 
and  a  portion  of  the  fused  mass  is  placed  on  a  silver  coin  and 
moistened  with  water  produce  a  brownish  or  black  stain  on 
the  coin. 

On  acidulating  a  solution  of  a  sulphite  with  hydrochloric 
acid,  sulphurous  anhydride  is  evolved,  which  may  be  recog- 
nized by  its  odor  of  burning  sulphur  and  by  its  action  upon 
moistened  potassium  iodate  starch-paste  paper,  the  latter  be- 
coming blue,  owing  to  the  iodine  separated  by  the  sulphurous 
anhydride  from  the  iodate  acting  upon  the  starch. 

Argentic  nitrate  precipitates  white  argentic  sulphite,  soluble 
in  nitric  acid.  On  boiling  the  precipitate  with  water,  it  is 
decomposed,  with  the  separation  of  finely-divided,  gray  metal- 
lic silver. 

To  detect  sulphurous  acid  in  the  presence  of  hyposulphur- 
ous  acid,  see  6,  page  62. 

Hyposulphurous  Acid.     (Hyposulphites.} 

Hyposulphites  when  fused  with  sodium  carbonate  on  char- 
coal and  a  portion  of  the  fused  mass  is  placed  on  a  silver 
coin  and  moistened  with  water  produce  a  brownish  or  black 
stain  on  the  coin. 

Hydrochloric  acid  or  sulphuric  acid  added  to  a  hyposul- 
phite causes  the  evolution  of  sulphurous  anhydride  (odor  of 
burning  sulphur)  and  a  milkiness  due  to  the  separation  of 
sulphur. 

Argentic  nitrate  produces  a  white  precipitate  of  argentic 
hyposulphite,  which  rapidly  changes  to  brown  and  finally  to 
t>lack  argentic  sulphide.  As  argentic  hyposulphite  is  soluble 
in  an  excess  of  a  hyposulphite  of  an  alkali,  precipitation 
occurs  only  when  an  excess  of  the  argentic  nitrate  is  added. 

To  detect  sulphuric  acid  and  other  acids  in  the  presence  of 


164 

hyposulphurous  acid,  the  latter  acid  must  be  decomposed  by 
gently  warming  with  hydrochloric  acid,  the  liquid  filtered, 
and  the  tests  for  sulphuric  acid  and  acids  other  than  hydro- 
chloric acid  made  in  the  filtrate. 

Phosphoric  Add.     (Phosphates.) 

Ammonium  chloride,  ammonium  hydroxide,  and  mag- 
nesium sulphate  (magnesia  mixture),  added  in  turn  to  a  solu- 
tion of  a  phosphate,  produce  a  white,  crystalline  precipitate 
of  ammonium  magnesium  phosphate. 

Ammonium  molybdate,  added  in  excess  with  a  consider- 
able quantity  of  nitric  acid,  produces  a  yellow  precipitate  of 
ammonium  phosphomolybdate. 

(If  arsenic  acid  is  present,  it  must  be  completely  removed 
by  precipitation  with  hydrogen  sulphide  before  testing  for 
phosphoric  acid.  With  reference  to  the  behavior  of  silicic 
acid  with  ammonium  molybdate,  see  3,  page  70.) 

Boric  Acid.     (Borates.) 

Turmeric  paper  dipped  in  an  aqueous  solution  of  boric 
acid,  or  of  a  borate  acidified  with  hydrochloric  acid,  and 
warmed  until  dry,  becomes  reddish  brown  in  color. 

Boric  acid  alone,  or  borates  placed  in  a  dish  and  moistened 
with  a  few  drops  of  concentrated  sulphuric  acid,  covered  with 
alcohol,  and  the  latter  ignited,  impart  a  greenish  color  to  the 
flame.  (Other  substances,  as  copper,  which  might  also  im- 
part a  green  color  to  the  flame  should  be  removed  before 
making  the  test.) 

Hydrofluoric  Acid.     (Fluorides.) 
Etches  glass  (see  4,  page  67). 

Carbonic  Acid.     (Carbonates^) 

On  adding  an  acid  to  a  carbonate,  effervescence  occurs,  due 
to  the  evolution  of  carbon  dioxide.  The  presence  of  carbon 


165 

dioxide  is  confirmed  by  the  production  of  a  white  turbidity 
or  precipitate,  due  to  the  formation  of  calcium  carbonate  with 
clear  calcium  hydroxide  solution  (see  2,  page  68). 

Silicic  Acid.     (Silicates.) 

A  portion  fused  in  a  bead  of  microcosmic  salt  yields  a  bead 
in  which  the  silica  is  not  dissolved,  but  swims  in  the  fused 
bead  as  small  opaque  particles  (see  4,  page  70). 

Arsenious  Acid.     (Arsenites.) 

Arsenic  Acid.     (Arseniates.) 

Chromic  Acid.     ( Chromates.) 

These  will  have  been  detected  in  the  preliminary  exam- 
ination and  in  the  examination  for  bases. 

Argentic  nitrate  added  to  a  solution  of  arsenious  acid,  fol- 
lowed by  the  addition  of  ammonium  hydroxide,  drop  by 
drop,  or  to  a  solution  of  an  arsenite,  produces  a  yellow, 
curdy  precipitate  of  argentic  arsenite,  soluble  in  ammonium 
hydroxide  and  in  nitric  acid. 

Argentic  nitrate  added  to  a  solution  of  arsenic  acid,  fol- 
lowed by  the  addition  of  ammonium  hydroxide,  drop  by 
drop,  or  to  a  solution  of  an  arseniate,  produces  a  reddish- 
brown  precipitate  of  argentic  arseniate,  soluble  in  ammonium 
hydroxide  and  in  nitric  acid. 

Arsenious  acid  may  be  detected  in  the  presence  of  arsenic 
acid  by  its  being  immediately  precipitated  as  arsenious  sul- 
phide by  hydrogen  sulphide,  whereas  arsenic  acid  is  pre- 
cipitated only  after  continuing  the  introduction  of  hydrogen 
sulphide  for  some  time. 

Arsenic  acid  is  detected  in  the  presence  of  arsenious  acid 
by  the  formation  of  a  white,  crystalline  precipitate  of  am- 
monium magnesium  arseniate  on  the  addition  of  magnesia 
mixture  (see  7,  page  28).  Arsenious  acid  does  not  produce  a 
precipitate  with  magnesia  mixture. 


166 

Chromic  acid  produces  a  yellow  precipitate  with  plumbic 
acetate  and  a  purplish-red  precipitate  with  argentic  nitrate 
(see  3,  page  71,  and  4,  page  72). 

Oxalic  Add.     (Oxalates.) 

Tartaric  Acid.     (Tartrates.) 

Produce  white  precipitates  with  calcium  chloride.  They 
may  be  distinguished  when  together  by  the  behavior  of  their 
calcium  salts :  calcium  oxalate  is  insoluble  and  calcium  tar- 
trate  soluble  in  acetic  acid. 

Hydrochloric  Acid.     (Chlorides.) 

Hydrobromic  Acid.     (Bromides.) 

Hydriodic  Acid.     (Iodides.) 

Hydrocyanic  Acid.     (Cyanides.) 

All  are  precipitated  by  argentic  nitrate  respectively  as 
chloride,  bromide,  iodide,  and  cyanide  of  silver,  and  are  dis- 
tinguished by  the  behavior  of  their  silver  salt  with  ammonium 
hydroxide.  Argentic  chloride  and  argentic  cyanide  are  easily 
soluble  in  dilute  ammonium  hydroxide.  Argentic  bromide 
is  soluble  in  concentrated  ammonium  hydroxide ;  argentic 
iodide  is  insoluble  in  ammonium  hydroxide. 

If  the  precipitate  produced  on  the  addition  of  argentic 
nitrate  is  insoluble  in  nitric  acid  but  soluble  in  ammonium 
hydroxide,  hydriodic  acid  is  absent,  but  hydrochloric  acid, 
hydrocyanic  acid,  and  hydrobromic  acid  may  be  present.  A 
test  for  hydrocyanic  acid  may  be  made  by  means  of  the 
Prussian-blue  reaction  (see  4,  page  78),  and  for  hydrobromic 
acid  with  chlorine- water  and  chloroform  or  carbon  disulphide 
(see  5,  page  75). 

If  neither  hydrobromic  acid  nor  hydrocyanic  acid  is  present, 
the  solubility  of  the  silver  precipitate  in  ammonium  hydrox- 
ide proves  the  presence  of  hydrochloric  acid.  If  hydrobromic 
acid  or  hydrocyanic  acid  is  present,  the  distillation  test  with 


167 

potassium  bichromate  and  sulphuric  acid  must  be  made  for 
hydrochloric  acid  (see  4,  page  74). 

If  the  precipitate  is  insoluble  or  only  partly  soluble  in 
ammonium  hydroxide,  the  presence  or  absence  of  hydriodic 
acid  must  be  established  by  means  of  chlorine-water  and 
chloroform  or  carbon  disulphide  (see  5,  page  76).  If  a  violet 
color  is  produced,  chlorine-water  is  added  drop  by  drop  until 
either  decolor ization  occurs  (absence  of  hydrobromic  acid)  or 
the  yellow  color,  due  to  the  presence  of  bromine  (which  was 
obscured  by  the  violet  color  produced  by  iodine),  appears  (see 
5,  page  75). 

The  test  for  hydrocyanic  acid  should  be  made  as  before 
described  (page  125).  The  distillation  test  for  the  detection 
of  hydrochloric  acid  is  to  be  employed  when,  in  addition  to 
hydriodic  acid,  hydrobromic  acid  or  hydrocyanic  acid  is 
present.  If  hydrobromic  acid  or  hydrocyanic  acid  -is  ab- 
sent, hydrochloric  acid  may  be  detected  in  the  presence  of 
hydriodic  acid  by  the  solubility  of  the  silver  precipitate  in 
ammonium  hydroxide. 

It  should  be  remembered  that  chloride,  bromide,  iodide, 
and  cyanide  of  silver  are  soluble  in  hyposulphites  of  the 
alkalies ;  therefore  in  the  presence  of  hyposulphites  the  hypo- 
sulphurous  acid  should  be  removed  by  gently  warming  with 
nitric  acid. 

As  argentic  nitrate  fails  to  produce  a  precipitate  in  solu- 
tions of  mercuric  cyanide,  the  presence  of  mercuric  cyanide 
must  be  proved  according  to  4,  page  111. 

Hydroferrocyanic  Acid.     (Ferrocyanides.} 

Ferric  chloride  produces  a  dark-blue  precipitate  of  ferric 
ferrocyanide  (Prussian  blue),  insoluble  in  acids  (see  5,  page  80). 

Cupric  sulphate  produces  a  precipitate  of  brownish-red 
cupric  ferrocyanide. 


168 

Hydroferricyanic  Acid.     (Ferricyanides.) 

Ferrous  sulphate  precipitates  blue  ferrous  ferricyanide 
(Turnbull's  blue),  insoluble  in  acids. 

Ferric  chloride  fails  to  produce  a  precipitate,  but  produces 
a  dark  coloration  in  the  liquid,  due  probably  to  the  produc- 
tion of  ferric  ferricyanide  (see  3,  page  80). 

Cupric  sulphate  precipitates  greenish-yellow  cupric  ferri- 
cyanide. 

Hydriodic  add  (iodides),  hydrobromic  acid  (bromides),  and 
hydrochloric  acid  (chlorides)  are  detected  in  the  presence  of 
hydroferrocyanic  acid  and  hydroferricyanic  acid  by  means  of 
chlorine-water  and  chloroform,  and  by  distillation  with  potas- 
sium bichromate  and  sulphuric  acid. 

To  detect  hydrocyanic  acid  in  the  presence  of  hydroferro- 
cyanic acid  and  hydroferricyanic  acid,  the  solution  is  acidu- 
lated with  hydrochloric  acid,  and  calcium  carbonate  is  imme- 
diately added  until  carbon  dioxide  ceases  to  be  evolved.  A 
test  for  hydrocyanic  acid  is  then  made  by  the  ammonium 
sulphocyanide  reaction  (see  5,  page  78).  The  hydrochloric 
acid  liberates  hydrocyanic  acid  as  well  as  hydroferrocyanic 
acid  and  hydroferricyanic  acid,  but  only  the  two  latter  pos- 
sess the  property  of  decomposing  carbonates  to  form  salts; 
hydrocyanic  acid,  therefore,  remains  in  the  free  state. 

Hydrogen  Sulphide.     (Sulphides.) 

The  presence  of  sulphides  is  detected  when  making  the 
preliminary  examination. 

A  soluble  sulphide  placed  on  a  clean  silver  coin  and 
moistened  with  a  few  drops  of  water  produces  a  brownish  or 
black  stain  on  the  coin. 

Nitric  acid  or  nitro-hydrochloric  acid  decomposes  sulphides, 
with  the  separation  of  sulphur ;  hydrochloric  acid  causes  the 


169 

evolution  of  hydrogen  sulphide  if  it  should  have  any  action 
at  all. 

Plumbic  acetate  produces  in  solutions  of  sulphides  a  black 
precipitate  of  plumbic  sulphide. 

Sodium  nitro-prusside  solutions  are  colored  violet  by  sul- 
phides, but  not  by  free  hydrogen  sulphide. 

Nitrous  Acid.     (Nitrites.) 

On  the  addition  of  an  acid  to  a  nitrite,  brownish-red  fumes 
of  nitrogen  dioxide  are  evolved. 

On  adding  a  few  drops  of  sulphuric  acid  to  a  solution  of 
a  nitrite,  cooling  the  liquid,  and  adding  ferrous  sulphate,  a 
brown  or  black  coloration  is  produced  (see  5,  page  82). 

Potassium  iodide  (or  cadmium  iodide),  starch  paste,  and  a 
few  drops  of  dilute  sulphuric  acid  added  to  a  solution  of  a 
nitrite  produce  a  blue  coloration  (see  6,  page  83). 

Before  testing  for  nitric  acid  in  the  presence  of  nitrous  acid, 
the  nitrous  acid  must  be  decomposed  by  being  boiled  a  suffi- 
cient length  of  time  with  a  solution  of  ammonium  chloride  : 


KNO2  +  NH4C1  =  KC1  +  N2  +  2H2O. 

Hypochlorous  Add.     (Hypochlorites.) 

Hydrochloric  acid  decomposes  hypochlorites,  with  the  evo- 
lution of  chlorine. 

Plumbic  acetate  produces  in  solutions  of  hypochlorites  at 
first  a  white  precipitate  of  plumbic  chloride,  which  soon 
becomes  yellow  and  finally  brown,  due  to  the  formation  of 
lead  dioxide  (see  3,  page  83). 

Nitric  Acid.     (Nitrates.} 

On  adding  a  small  quantity  of  concentrated  sulphuric  acid 
to  a  solution  of  a  nitrate,  cooling,  and  placing  a  crystal  of 
ferrous  sulphate  in  the  liquid,  a  brownish  or  black  ring  is 
formed  around  the  crystal  (see  3,  page  84). 
H  15 


170 

With  potassium  iodide  (or  cadmium  iodide),  starch  paste, 
and  dilute  sulphuric  acid  nitrates  do  not  produce  a  blue 
discoloration  unless  a  fragment  of  metallic  zinc  is  added. 
(Distinction  from  nitrites.  See  4,  page  84.) 

Before  testing  for  nitric  acid  in  the  presence  of  hydriodic 
acid  or  hydrobromic  acid,  the  two  latter  acids  must  be  re- 
moved by  precipitation  with  argentic  sulphate  or  with  plumbic 
acetate,  the  precipitate  filtered  off,  and  the  tests  for  nitric  acid 
made  in  the  filtrate. 

Chloric  Acid.     (Chlorates.) 

On  warming  a  solution  of  a  chlorate  with  hydrochloric 
acid  the  liquid  becomes  greenish  yellow  in  color,  and  greenish- 
yellow  fumes  of  a  mixture  of  chlorine  and  chlorine  tetroxide 
are  evolved. 

Concentrated  sulphuric  acid  poured  upon  a  very  small 
portion  of  a  solid  chlorate  causes  the  evolution  of  chlorine 
tetroxide  (see  4,  page  86). 

Chlorates  in  the  solid  state  on  being  strongly  heated  are 
converted  into  chlorides.  On  dissolving  the  residue  in  water 
and  testing  for  a  chloride  with  argentic  nitrate,  a  white  pre- 
cipitate of  argentic  chloride  will  be  produced.  (A  chlorate 
itself,  free  from  chlorides,  does  not  yield  a  precipitate  with 
argentic  nitrate.) 

Acetic  Acid.     (Acetates.') 

On  adding  ferric  chloride  to  a  solution  of  an  acetate  and 
boiling  the  liquid,  a  brownish-red  precipitate  of  basic  ferric 
acetate  is  formed. 

Sulphuric  acid  added  to  an  acetate  and  the  liquid  warmed 
liberates  acetic  acid,  which  is  recognized  by  its  odor  of  vinegar. 

Alcohol  added  to  a  cooled  solution  of  an  acetate  containing 
free  sulphuric  acid  and  then  warmed  produces  acetic  ether, 
which  is  recognized  by  its  apple-like  odor  (see  6,  page  87). 


APPENDIX. 


BEHAVIOE  OF  THE   COMPOUNDS   OF   THE   RAKE 
ELEMENTS. 


THE  deportment  of  the  rare  elements  and  their  compounds 
when  subjected  to  the  usual  preliminary  examination,  as  well 
as  the  behavior  of  these  elements  with  the  ordinary  group 
reagents,  will  be  treated  of  in  the  following  pages.  It  is  not 
intended  to  give  a  detailed  description  of  the  separation  of 
the  rare  elements  from  one  another  or  from  the  more  fre- 
quently occurring  elements,  but  in  the  latter  part  of  the 
appendix  a  few  examples  are  given  of  the  separation  of  the 
rare  elements  in  minerals  which  may  be  easily  procured. 


I.    BEHAVIOR    IN   THE    PRELIMINARY    EXAMINA- 
TION. 

(a)  On  heating  the  substance  in  a  glass  reduction-tube : 
Titanic  acid  becomes  yellow  to  brown. 
Niobic  acid  becomes  yellow. 
Tantalic  o,cid  becomes  pale  yellow. 

Selenium  and  selenides  yield  a  reddish-brown  sublimate  : 
a  portion  heated  in  a  tube  open  at  both  ends  and  held 
obliquely  in  the  flame  gives  a  radish-like  odor. 

171 


172 

Tellurium  sublimes ;  heated  in  a  tube  open  at  both  ends, 
it  burns,  producing  dense  white  clouds. 

(6)  On  heating  the  substance  with  the  blowpipe  flame  on 
charcoal,  there  are  produced  : 
Fused  metallic  globules : 

Gold :  yellow,  ductile,  without  incrustation. 

Thallium :  white,  ductile,  yellow  incrustation. 

Indium :  white,  ductile,  white  incrustation. 
Incrustation,  without  metallic  globule  : 

Tellurium. 
Infusible  metallic  masses : 

Tungsten, 

Molybdenum, 

Platinum, 

Palladium,  etc. 
White  masses 
(When  heated  with  cobaltous  nitrate  solution) : 

Titanic  acid  becomes  yellowish  green. 

Niobic  add  becomes  dirty  green. 

Tantalie  acid  becomes  flesh  color. 

Beryllia  becomes  gray. 
Brownish-red  masses : 

Selenium  compounds. 

Tellurium  compounds. 

When  placed  on  a  silver  coin  and  moistened  with  water, 
a  brown  or  black  stain  is  produced  on  the  coin. 
When  treated  with  hydrochloric  acid,  hydrogen  sele- 
nide  and  hydrogen  telluride  are  evolved. 

(c)  On  fusing  the  substance  in  a  bead  of  microcosmic  salt 
the  following  colored  beads  result  in  the 


173 

Oxidizing  Flame. 
Uranium :  yellow  when  hot, 

yellowish  green  when 

cold. 
Cerium:    reddish    yellow    when 

hot, 

lighter  reddish  yellow 
to     colorless     when 
cold. 
Didymium :  colorless. 

Titanium :  colorless. 
Niobium:  colorless. 
Tungsten:  colorless. 
Molybdenum :  colorless. 
Vanadium :  colorless. 


Reducing  Flame. 
Green. 


Colorless. 


Amethyst  changing 

to  violet. 
Violet, 

Blue  or  violet. 
Blue. 
Black. 
Green. 


Gold  and  platinum  are  not  dissolved  in  the  bead  of  micro- 
cosmic  salt. 


(d)  Examination  in  the  flame. 
The  non-luminous  flame  is  colored  by 
Lithium :  carmine-red. 
Rubidium:  violet. 
Caesium:  violet. 
Indium :  bluish  violet. 
Selenium :  ultramarine-blue. 
Tellurium :  blue  bordered  with  green. 
Thallium:  intense  green. 
Molybdic  acid :  yellowish  green. 

Lithium,  rubidium,  ccesium,  indium,  thallium,  and  gallium 
are  best  detected  by  means  of  the  spectroscope.  Erbium  and 
didymium  also  furnish  absorption  spectra. 

15* 


174 


II.  BEHAVIOR  WITH   THE  GROUP   REAGENTS. 

FIRST   GROUP. 

Hydrochloric  acid  precipitates : 

Thallium :  as  white  curdy  T1C1,  thallous  chloride,  solu- 
ble with  difficulty  in  water. 
From  alkaline  solutions : 

Molybdic  acid :  as  white  H2MoO4,  molybdic  acid,  soluble 
in  an  excess  of  hydrochloric  acid. 

Tungstic  acid :  as  white  H2WO4,  tungstic  acid,  insoluble 
in  an  excess  of  hydrochloric  acid ;  becomes  yellow  on 
boiling. 

Tantalic  acid :  as  white  HTaO3,  tantalic  acid,  soluble  in 
an  excess  of  hydrochloric  acid,  producing  opalescence 
in  the  liquid. 

SECOND  GROUP. 

Hydrogen  sulphide  precipitates : 

Palladium :  as  black  PdS,  palladious  sulphide.  1  |  § 
Osmium :  as  brownish-black  OsS,  osmic  sulphide.  g  & 
Rhodium :  as  brown  Rh2S3,  rhodic  sulphide.  |-  ~ 

Ruthenium :  as  brown  Ru2S3,  ruthenic  sulphide.      J   f  1 
(The  liquid  at  first  becomes  azure-blue  in  color.) 
Gold :  as  black  Au2S3,  auric  sulphide.  ] 

Platinum:  as  brownish-black  PtS2,  platinic  sulphide.      | 
Indium :  as  brown  Ir2S3,  iridic  sulphide. 
Molybdenum :  as  brown  MoS3,  molybdic  sulphide. 
(A  small  quantity  of  hydrogen  sulphide  colors  the  j-  s 

solution  blue.) 
Selenium :  as  yellow,  which  on  warming  changes  to     ,| 

reddish-yellow  SeS2,  selenic  sulphide. 
Tellurium :  as  brown  TeS2,  telluric  sulphide. 
The  solution  may  become  blue  in  color  if  compounds  of 

tungsten  or  vanadium  are  present. 


175 


THIRD  GROUP. 

Ammonium    hydroxide   in   the    presence   of    ammonium 
chloride  precipitates : 

Uranium:   as   yellow    (NH4)2Ur2O7(?),  ammonium 

uranate. 
Indium :  as  white  In(OH)3,  indie  hydroxide,  soluble 

in  NaOH. 
Beryllium:  as  white  Be(OH)2,  beryllic  hydroxide, 

soluble  in  NaOH. 
Zirconium:  as  white  Zr(OH)4,  zirconic  hydroxide, 

insoluble  in  NaOH. 

Thorium :  as  white  Th(OH)4,  thoric  hydroxide,  in- 
soluble in  NaOH. 

Yttrium:   as  white  Y(OH)2,  yttric  hydroxide,  in- 
soluble in  NaOH. 
Cerium :          ~\ 

Lanthanum :  >•  as  basic  salts. 
Didymium :    . 

Titanium :  as  white  Ti(OH)4,  titanic  hydroxide. 
Tantalum :  as  white  TaO2(OH),  acid  tantalic  hydroxide, 

or  as  an  acid  ammonium  salt. 

Niobium :  as  white  NbO2(OH),  acid  niobic  hydroxide,  or 
as  an  acid  ammonium  salt. 


FOURTH   GROUP. 

Ammonium  sulphide  precipitates : 

Thallium :  as  black  T1S,  thallous  sulphide. 

If  the  nitrate  from  the  Fourth  Group  precipitate  is  treated 
with  hydrochloric  acid,  there  will  be  precipitated : 
Tungsten :  as  brown  WS3,  tungstic  sulphide. 


176 

Vanadium:   as   brown  vanadium   sulphide,  containing 

oxygen  and  varying  in  composition. 
Molybdenum:   (if  present)   as   brown   MoS3,  molybdic 

sulphide. 

FIFTH  GROUP. 

In  this  group  may  be  found  : 

Lithium. 

Ccesium. 

Rubidium. 
(To  be  detected  by  means  of  the  spectroscope.) 


III.  EXAMPLES  FOR  PRACTICE, 

WOLFRAMITE. 

Wolframite  may  be  recognized  by  the  blue  color  it  imparts 
to  the  bead  of  microcosmic  salt  in  the  reducing  flame,  and  by 
the  yellow  residue  of  tungstic  acid  remaining  when  the  finely- 
pulverized  mineral  is  boiled  with  hydrochloric  acid. 

The  finely-pulverized  wolframite  is  boiled  with  concentrated 
hydrochloric  acid,  and  a  few  drops  of  concentrated  nitric 
acid  are  added  from  time  to  time,  until  the  undissolved  resi- 
due is  pure  yellow  in  color  and  does  not  undergo  further 
change.  Tungstic  acid  remains  undissolved  as  a  yellow 
powder,  while  the  bases  enter  into  solution  as  chlorides.  The 
liquid  containing  the  insoluble  residue  is  evaporated  to  dry- 
ness  on  a  water-bath,  the  residue  extracted  with  water  con- 
taining a  small  quantity  of  hydrochloric  acid,  filtered,  and 
the  filtrate  tested  for  bases. 

The  insoluble  residue  contains  tungstic  acid,  and  frequently 
silicic  acid  and  niobic  acid.  The  residue  is  treated  with  am- 
monium hydroxide,  which  dissolves  the  tungstic  acid  as  an 


177 

ammonium  salt,  leaving  an  undissolved  residue  consisting  of 
silicic  acid  and  possibly  niobic  acid.  This  residue  is  thor- 
oughly washed  with  ammonium  hydroxide,  to  render  it  free 
from  tungstic  acid,  and  then  tested  in  a  bead  of  microcosmic 
salt  for  niobic  acid. 

The  ammoniacal  solution  containing  ammonium  tungstate 
should  give  the  following  reactions  : 

Hydrochloric  acid  precipitates  white  H2WO4,  tungstic  acid, 
which,  on  boiling,  becomes  yellow. 

Metallic  zinc  and  an  excess  of  hydrochloric  acid  impart 
to  the  precipitate  of  tungstic  acid  a  blue  color  changing  to 
brown  (due  to  the  formation  of  lower  oxides  of  tungsten). 

Stannous  chloride  produces  a  yellow  precipitate ;  on  adding 
hydrochloric  acid  and  warming,  the  yellow  color  changes  to 
blue. 

Ammonium  sulphide  added  to  the  solution  of  ammonium 
tungstate  produces  no  precipitate,  but  forms  the  soluble 
sulpho-salt  (NH4)2WS4.  On  adding  hydrochloric  acid  to  this 
solution,  brown  WS2,  tungstic  sulphide,  is  precipitated.  The 
supernatant  liquid  is  generally  blue  in  color. 

MOLYBDENITE. 

Molybdenite,  when  fused  in  a  bead  of  microcosmic  salt, 
yields  a  colorless  bead  in  the  oxidizing  flame  and  a  black 
bead  in  the  reducing  flame.  It  imparts  a  yellowish-green 
color  to  the  non-luminous  flame.  When  heated  on  charcoal, 
it  yields  a  reddish-brown  mass.  It  is  soluble  in  nitro-hydro- 
chloric  acid,  imparting  a  green  color  to  the  liquid.  On 
evaporating  the  excess  of  acid,  diluting  with  water,  and  con- 
ducting hydrogen  sulphide  into  the  solution,  a  blue  coloration 
is  produced,  and  gradually  brownish-black  MoS3,  molybdic 
sulphide,  is  precipitated.  Molybdic  sulphide  is  soluble  in 


178 

ammonium  sulphide,  which  dissolves  it  as  a  sulpho-salt, 
(NH4)2MoS4,  from  which  solution  it  is  reprecipitated  by 
hydrochloric  acid  as  MoS3,  molybdic  sulphide. 

The  nitrate  from  the  precipitate  produced  by  the  intro- 
duction of  hydrogen  sulphide  may  still  contain  molybdenum 
in  solution ;  therefore,  before  testing  for  the  metals  of  the 
Fifth  Group,  ammonium  hydroxide  is  added  to  the  solution, 
which  is  gently  warmed,  filtered  if  a  precipitate  be  formed, 
and  the  solution,  which  now  contains  (NH4)2MoS4,  is  treated 
with  hydrochloric  acid,  which  precipitates  the  remaining 
molybdenum  as  molybdic  sulphide. 

The  molybdic  sulphide  reprecipitated  in  the  Second  Group 
from  the  ammonium  sulphide  solution  by  hydrochloric  acid 
is  collected  on  a  filter,  dried,  and  placed  in  an  uncovered 
crucible,  which  is  placed  obliquely  over  the  flame  and  gently 
heated,  whereby  the  molybdic  sulphide  is  oxidized  and  con- 
verted into  molybdic  acid,  with  the  evolution  of  sulphurous 
anhydride.  When  the  sulphurous  anhydride  ceases  to  be 
evolved,  the  yellow  residue  is  dissolved  in  ammonium  hy- 
droxide and  the  resulting  solution  of  ammonium  molybdate 
tested  as  follows :  a  small  portion  of  the  solution  is  tested 
for  copper  with  a  few  drops  of  ammonium  sulphide,  and  the 
remainder  of  the  solution  is  used  in  making  the  tests  for 
molybdenum.  (The  precipitated  molybdic  sulphide  obtained 
from  the  Fourth  Group  is  heated  in  an  uncovered  crucible 
and  treated  in  the  same  manner.) 

Hydrochloric  acid  causes  the  precipitation  of  white  ILjMoO^ 
molybdic  acid,  soluble  in  an  excess  of  hydrochloric  acid. 
Stannous  chloride  produces  in  the  hydrochloric  acid  solution 
of  molybdic  acid  a  blue  coloration,  changing  to  green  and 
finally  to  brown  •  metallic  zinc  produces  a  similar  coloration, 
but  not  so  promptly.  The  change  in  color  in  the  two  pre- 
ceding reactions  is  due  to  the  reduction  of  molybdic  acid. 


179 

Ammonium  sulphocyanide  added  to  the  ammoniacal  solu- 
tion, followed  by  the  addition  of  hydrochloric  acid  and  zinc, 
produces  a  carmine-red  coloration  (in  consequence  of  reduction 
with  the  formation  of  sulphocyanides  of  the  oxides). 

Concentrated  nitric  acid  and  sodium  hydrogen  phosphate 
added  to  the  ammoniacal  solution  precipitate  yellow  am- 
monium phosphomolybdate. 

WULFENITE. 

Wulfenite,  when  heated  in  the  blowpipe  flame  on  charcoal, 
yields  a  globule  of  metallic  lead ;  when  fused  in  a  bead  of 
microcosmic  salt,  it  yields  a  colorless  bead  in  the  oxidizing 
flame  and  a  black  bead  in  the  reducing  flame. 

Wulfenite  is  soluble  in  hydrochloric  acid  with  the  separa- 
tion, upon  cooling,  of  crystalline  plumbic  chloride.  The 
hydrochloric  acid  solution  yields  with  hydrogen  sulphide  in 
the  Second  Group  a  precipitate  of  molybdic  sulphide,  soluble 
in  ammonium  sulphide,  thus  furnishing  a  means  of  separating 
it  from  plumbic  sulphide,  which  is  insoluble  in  ammonium 
sulphide.  After  precipitating  the  Fourth  Group,  the  reddish- 
brown  nitrate  is  treated  with  hydrochloric  acid  to  precipitate 
the  remainder  of  molybdic  sulphide. 

The  molybdic  sulphide  is  further  examined  as  given  under 
Molybdenite,  page  134. 

URANINITE  (PITCHBLENDE). 

Uraninite,  when  fused  in  the  bead  of  microcosmic  salt, 
yields  a  yellow  bead  in  the  oxidizing  flame  and  a  green  bead 
in  the  reducing  flame ;  treated  with  nitric  acid  it  dissolves, 
leaving  a  residue  of  silicic  acid  and  insoluble  oxides  (see  page 
110).  The  nitric  acid  solution  yields  in  the  Third  Group  a 
precipitate  containing  uranium,  the  uranium  being  precipi- 
tated as  yellow  ammonium  uranate.  In  order  to  separate 


180 

uranium  the  precipitate  of  the  Third  Group  is  digested  at  a 
moderate  heat  with  a  concentrated  solution  of  ammonium 
carbonate ;  uranium  enters  into  solution  as  uranyl  ammonium 
carbonate,  UrO2CO3  ((NH4)2CO3)2,  imparting  a  yellow  color 
to  the  solution. 

The  oxides  of  the  other  metals  remain  undissolved,  and 
after  being  collected  on  a  filter  may  be  examined  according 
to  the  usual  scheme  of  analysis. 

To  detect  uranium  a  portion  of  the  yellow  filtrate  contain- 
ing uranyl  ammonium  carbonate  is  acidulated  with  acetic 
acid  and  treated  with  potassium  ferrocyanide :  a  reddish- 
brown  precipitate  of  (UrO2)2  Fe(CN)6,  uranyl  ferrocyanide, 
indicates  the  presence  of  uranium.  The  remainder  of  the 
solution  of  uranyl  ammonium  carbonate  is  carefully  concen- 
trated on  a  water-bath,  and  on  cooling  glistening  yellow 
crystals  of  uranyl  ammonium  carbonate  separate,  which  when 
strongly  ignited  leave  a  residue  of  dark-green  uranous-uranic 
oxide,  Ur3O8. 

On  treating  the  filtrate  containing  ammonium  sulphide 
from  the  precipitate  of  the  Fourth  Group  with  hydrochloric 
acid,  nickelous  sulphide  together  with  vanadic  sulphide  may 
be  precipitated.  If  a  precipitate  is  obtained  by  treatment  with 
hydrochloric  acid,  it  is  collected  on  a  filter,  washed,  dried, 
mixed  with  potassium  nitrate,  fused,  and  the  resulting  fused 
mass  extracted  with  water,  whereby  vanadium  as  an  acid 
vanadium  salt  enters  into  solution.  On  filtering,  neutralizing 
the  filtrate  with  nitric  acid,  and  adding  a  concentrated  solution 
of  ammonium  chloride,  vanadic  acid  in  combination  with 
ammonium  is  gradually  precipitated  as  a  white  ammonium 
salt.  On  collecting  the  precipitate  on  a  filter,  dissolving  in 
water,  and  adding  a  small  quantity  of  hydrochloric  acid,(1) 

1  The  solution  becomes  yellow  or  red  in  color. 


181 

followed  by  the  addition  of  metallic  zinc,  the  solution  becomes 
blue  in  color. 

RUTILE  (TITANIFEROUS  IRON). 

Rutile,  when  fused  in  a  bead  of  microcosmic  salt  in  the 
reducing  flame,  yields  a  violet-  to  blood-red-colored  bead. 
Fused  in  the  oxidizing  flame  (when  a  sufficient  quantity 
of  the  mineral  is  employed)  it  yields  microscopic  tabular 
crystals  of  anatase  (TiO2). 

The  mineral  is  best  decomposed  by  being  fused  with  acid 
potassium  sulphate  at  not  too  high  a  temperature.  The  fused 
mass  after  cooling  is  pulverized  and  dissolved  in  cold  water : 
the  titanium  enters  into  solution  as  sulphate.  The  liquid  is 
filtered  and  a  portion  of  the  filtrate  tested  with  metallic  zinc 
or  tin  for  titanic  acid  :  in  the  presence  of  titanic  acid  a 
pale  violet  or  a  blue  coloration  is  imparted  to  the  solution 
and  afterwards  a  blue  precipitate  separates  which  gradually 
changes  to  white. 

On  boiling  the  remainder  of  the  precipitate  for  some  time, 
meta-titanic  acid  separates  as  a  white  powder.  The  meta- 
titanic  acid  is  filtered  off  and  the  filtrate  diluted  with  water 
and  again  boiled  and  filtered.  The  filtrate  is  then  tested  for 
the  remaining  bases  in  the  usual  manner. 

BERYL. 

Beryl,  when  fused  in  a  bead  of  microcosmic  salt,  slowly 
dissolves  without  the  formation  of  a  skeleton  of  silica.  The 
fragment  of  beryl  remains  in  the  bead  of  microcosmic  salt 
and  gradually  diminishes  in  size,  forming,  on  cooling,  an 
opalescent  bead.  Varieties  of  beryl  containing  chromium 
(for  example,  emeralds)  impart,  a  green  color  to  the  bead. 

As  beryl  is  insoluble  in  acids,  it  must  be  decomposed  by 
fusing  with  sodium  potassium  carbonate.  The  fused  mass  is 

16 


182 

treated  with  hydrochloric  acid  and  evaporated  to  dryness  on 
a  water-bath,  in  order  to  separate  silicic  acid.  The  residue 
is  extracted  with  water  containing  a  small  quantity  of  hydro- 
chloric acid  and  filtered ;  the  filtrate  contains  BeCl2,  beryllium 
chloride.  On  the  addition  of  ammonium  hydroxide  to  the 
filtrate,  Be(OH)2,  beryllium  hydroxide,  separates  as  a  white 
precipitate,  and  is  collected  on  a  filter  and  dissolved  in  an 
excess  of  sodium  hydroxide.  The  sodium  hydroxide  solution 
contains  sodium  aluminate  and  sodium  beryllate,  and  may 
also  contain  sodium  chromite,  in  which  case  the  solution 
would  be  green  in  color. 

If  chromium  is  not  present,  the  solution  is  treated  with  a 
considerable  quantity  of  ammonium  chloride,  which  precipi- 
tates aluminium  hydroxide  and  beryllium  hydroxide.  On 
boiling  the  liquid  for  some  time,  beryllium  hydroxide  enters 
into  solution  as  beryllium  chloride,  with  the  evolution  of 
ammoniacal  gas,  while  aluminium  hydroxide  remains  un- 
dissolved,  is  collected  on  a  filter,  and,  when  heated  with 
cobaltous  nitrate  on  charcoal,  yields  a  blue  mass.  The  ni- 
trate, which  contains  beryllium  chloride,  is  treated  with 
ammonium  hydroxide  to  precipitate  beryllium  hydroxide. 
Beryllium  hydroxide  is  soluble  in  an  excess  of  ammonium 
carbonate,  and  from  this  solution  it  separates  on  boiling  as  a 
basic  beryllium  carbonate.  The  beryllium  hydroxide,  when 
heated  with  cobaltous  nitrate  in  the  oxidizing  flame  on  char- 
coal, yields  a  gray  mass. 

If  chromium  is  present,  the  solution  is  diluted  with  water 
and  boiled  for  some  time :  aluminium  hydroxide  remains  in 
solution,  while  beryllium  hydroxide  and  chromium  hydroxide 
are  precipitated.  The  precipitate  is  collected  on  a  filter, 
dried,  and  the  beryllium  hydroxide  separated  from  the  chro- 
mium hydroxide  by  fusing  with  a  mixture  of  sodium  carbon- 
ate and  potassium  nitrate.  On  extracting  the  yellow  fused 


183 

mass  with  water,  beryllium  oxide  remains  undissolved,  while 
chromium  enters  into  solution  as  a  chromate  of  the  alkali. 

CERITE. 

Cerite,  heated  in  the  blowpipe  flame  on  charcoal,  is  infusi- 
ble, but  becomes  dirty  yellow  in  color.  Fused  in  a  bead  of 
microcosmic  salt,  it  yields  in  the  oxidizing  flame  a  reddish- 
yellow  bead,  and  in  the  reducing  flame  a  colorless  bead, 
together  with  a  skeleton  of  silica.  On  heating  a  portion  of 
the  finely-pulverized  mineral  with  hydrochloric  acid,  diluting 
with  water,  filtering,  and  adding  oxalic  acid  to  the  filtrate,  a 
white  precipitate  is  produced. 

On  heating  the  mineral  with  concentrated  hydrochloric 
acid,  evaporating  to  dryness  on  a  water-bath,  and  extracting 
the  residue  with  water  and  a  few  drops  of  hydrochloric  acid, 
the  bases  enter  into  solution  while  silicic  acid  remains  undis- 
solved. 

In  the  Second  Group,  in  addition  to  other  metals,  molyb- 
denum may  be  precipitated  as  molybdic  sulphide.  (See 
Molybdenite,  page  134.) 

Cerium,  lanthanum,  and  didymium  are  precipitated  by 
ammonium  hydroxide  in  the  Third  Group  as  hydroxides : 
Ce(OH)2,  La(OH)2,  and  Di(OH)2.  Cerium  hydroxide  and 
lanthanum  hydroxide  are  white.  The  former  when  exposed 
to  the  air  oxidizes  and  becomes  yellow  ;  didymium  hydroxide 
is  pink  in  color.  On  collecting  the  precipitate  of  the  Third 
Group  on  a  filter,  dissolving  in  hydrochloric  acid,  and  add- 
ing oxalic  acid,  cerium,  lanthanum,  and  didymium  are  pre- 
cipitated as  white  oxalates  insoluble  in  dilute  acids;  the 
filtrate  from  the  precipitate  of  oxalates  may  be  examined  for 
the  remaining  bases  of  the  Third  Group. 

The  oxalates  of  cerium,  lanthanum,  and  didymium  when 
ignited  yield  a  brown  residue  consisting  of  a  mixture  of 


184 

oxides  (Ce3O4,  LaO,  and  DiO).  On  heating  a  portion  of 
this  mixture  of  oxides  with  concentrated  sulphuric  acid,  sul- 
phates are  formed  which  are  soluble  in  water  and  impart  a 
yellow  color  to  the  liquid.  In  this  solution  concentrated 
potassium  sulphate  produces  a  lemon-yellow  precipitate  con- 
sisting of  a  mixture  of  double  salts. 

The  remainder  of  the  mixture  of  oxides  is  treated  with 
hydrochloric  acid  and  alcohol  and  then  heated :  the  oxides 
are  dissolved  thereby,  with  the  formation  of  chlorides  (CeCl2, 
LaCl2,  DiCl2).  If  didymium  is  present,  on  passing  a  ray  of 
light  through  the  solution,  the  spectrum  shows  dark  absorp- 
tion bands  (four  between  Frauenhofer's  lines  D  and  F  and 
two  between  F  and  G). 

On  adding  sodium  acetate  and  passing  chlorine  through 
the  solution,  or  on  the  addition  of  sodium  hypochlorite,  light- 
yellow  Ce3O7H6,  cerium  hydroxide,  is  precipitated,  which  is 
soluble  when  warmed  with  hydrochloric  acid,  forming  CeCl2, 
with  the  evolution  of  chlorine.  (For  the  separation  of 
cerium,  lanthanum,  and  didymium  the  reader  is  referred  to 
more  extensive  works  on  qualitative  analysis.) 

ZIRCON   (HYACINTH). 

Zircon,  heated  in  the  blowpipe  flame  on  charcoal,  is  infusi- 
ble, but  becomes  lighter  in  color.  It  is  not  dissolved  in  the 
bead  of  microcosmic  salt. 

It  is  decomposed  by  being  fused  for  some  time  with  sodium 
potassium  carbonate.  The  fused  mass  is  treated  with  hydro- 
chloric acid,  evaporated  to  dryness  on  a  water-bath  (to  render 
the  silica  insoluble),  the  residue  extracted  with  water  and 
hydrochloric  acid  and  filtered.  The  filtrate  contains  zirco- 
nium as  zirconium  chloride.  From  this  solution  the  zirco- 
nium is  precipitated  by  ammonium  hydroxide  in  the  Third 
Group  as  Zr(OH)4,  zirconium  hydroxide.  Zirconium  hy- 


185 

droxide  is  insoluble  in  sodium  hydroxide,  but  soluble  in 
ammonium  carbonate.  From  the  solution  in  ammonium 
carbonate  it  is  reprecipitated  by  boiling. 

On  dissolving  a  portion  of  this  precipitate  in  sulphuric 
acid  and  adding  a  concentrated  solution  of  potassium  sulphate, 
a  white  double  salt  of  zirconium  is  precipitated. 

The  hydrochloric  acid  solution  is  not  precipitated  by  oxalic 
acid,  but  the  neutral  solution  is  precipitated  by  ammonium 
oxalate ;  the  precipitate  redissolves  in  an  excess  of  ammonium 
oxalate.  Turmeric  paper,  moistened  with  the  hydrochloric 
acid  solution,  becomes  reddish  brown  in  color  when  dry. 

LEPIDOLITE. 

Lepidolite  when  fused  in  a  bead  of  microcosmic  salt  yields 
a  skeleton  of  silica.  When  placed  on  a  platinum  wire  and 
held  in  the  non-luminous  flame  it  imparts  a  carmine-red  color 
to  the  flame,  especially  after  moistening  the  lepidolite  with  a 
few  drops  of  hydrochloric  acid.  Treated  with  concentrated 
sulphuric  acid  it  responds  to  the  fluorine  reactions  (see  4,  page 
67,  and  5,  page  68). 

A  portion  of  the  mineral  is  heated  in  a  platinum  crucible 
(without  the  addition  of  carbonates  of  the  alkalies  as  a  flux) 
until  melted.  The  fused  mass  is  pulverized  and  then  decom- 
posed by  being  boiled  with  concentrated  hydrochloric  acid. 
The  solution  is  evaporated  to  dryness  on  a  water-bath  to 
render  the  silica  insoluble;  the  residue  is  extracted  with 
water  and  a  few  drops  of  hydrochloric  acid,  the  insoluble 
silica  filtered  oif,  and  the  filtrate  examined  for  bases. 

Lithium  belongs  to  the  Sixth  Group.  The  hydrochloric 
acid  filtrate,  obtained  as  described  above,  is  treated  with  am- 
monium carbonate  to  precipitate  the  metals  of  the  Fifth 
Group,  and  with  sodium  hydrogen  phosphate  to  precipitate 
magnesium,  filtered,  the  filtrate  treated  with  barium  chloride, 

16* 


186 

and  the  liquid  again  filtered.  The  filtrate  now  contains,  in 
addition  to  the  excess  of  barium  chloride,  the  alkaline  metals 
as  chlorides.  The  liquid  is  evaporated  to  dryness,  the  residue 
gently  heated  over  a  free  flame  to  expel  ammonium  chloride, 
and  then  placed  in  a  small  flask  and  extracted  with  a  mixture 
of  alcohol  and  ether.  Lithium  chloride  enters  into  solution, 
while  the  chlorides  of  the  other  metals  remain  undissolved. 

The  alcoholic  solution  is  filtered  and  the  filtrate  evaporated 
to  dryness  on  a  water-bath ;  the  residue  remaining  consists 
of  lithium  chloride,  which  is  recognized  by  its  imparting  a 
carmine-red  color  to  the  non-luminous  flame  and  by  the 
examination  with  the  spectroscope.  The  residue,  insoluble 
in  the  mixture  of  alcohol  and  ether,  is  dissolved  in  water, 
and  sulphuric  acid  added  to  the  solution  to  precipitate  barium 
as  barium  sulphate,  which  is  filtered  off  and  the  filtrate  ex- 
amined for  potassium  and  sodium. 


INDEX. 


PAGE 

Acetates 86,  1 70 

Acetic  acid 86,  170 

Acid,  acetic     86,  170 

arsenic 26 

arsenious 21 

boric 65,  164 

carbonic 68,  164 

chloric 85,  170 

chromic 71,  165 

ferricyanic 80,  168 

ferrocyanic 79,  168 

hydriodic      75,  166 

hydrobromic 74,  166 

hydrochloric 73,  166 

hydrocyanic 77,  166 

hydroferricyanic 80,  168 

hydroferrocyanic IT-  .:  .     79,  167 

hydrofluoric 67 

hydrofluosilicic 60,  162 

hypochlorous 83,  169 

hyposulphurous      63,  163 

molybdic 173 

niobic .    172 

nitric ^    , 84,  169 

nitrous      82,  169 

oxalic ' 87 

phosphoric 64,  164 

silicic 69,  165 

sulphuric 59,  162 

sulphurous 61,  163 

sulphydric 81,  168 

tantalic 172 

187 


188 

PAGE 

Acid,  tartaric gg 

thiosulphuric 53 

titanic .172 

Acid  sulphides,  separation  of 135 

Acids,  behavior  with  group  reagents 160 

examination  for 158 

preliminary  tests  for 99 

Aluminium 41 

Ammonium 55 

carbonate 50 

Antimony 28 

Marsh's  test  for 30 

Reinsch's  test  for 30 

in  antimonic  condition      31 

in  antimonious  condition      28 

Arsenic 21 

Marsh's  test  for 22 

Reinsch's  test  for 25 

in  arsenic  condition 26 

in  arsenious  condition 21 

Arsenic  acid 26 

Arsenious  acid 21 


Barium 50 

Bases,  detection  of,  in  the  Wet  Way 116 

precipitation  of  groups ' 117 

properties  of 9 

separation  of  First  Group 129 

Second  Group .    .    130 

Third  Group 139 

Fourth  Group 146 

Fifth  Group /v: 148 

Sixth  Group 152 

Basic  sulphides,  separation  of 135 

Beryl 181 

Beryllium ' 175 

Bismuth .    .   v 20 

Borates 65,  164 

Boric  acid 65,  164 

Bromides  .    .     74,  166 


189 

PAGE 

Cadmium 35 

Caesium 176 

Calcium 52 

Carbonates 68,  164 

Carbonic  acid 68,  164 

Cerite 183 

Cerium 175 

Charcoal,  examination  on 93 

Chlorates 85,  170 

Chloric  acid 85,  170 

Chlorides 73,  166 

Chromates * 71,  165 

Chromium 42 

Cobalt 47 

Copper 17 

Cyanides 77,  111,  166 

Detection  of  bases  in  the  Wet  Way 116 

Didymium 175 

Dissolving  metals  and  alloys 110 

oxides  and  salts 104 

Everett's  salt 39,80 

Examination  by  microcosmic  salt 97 

for  acids    .    , 158 

in  the  flame 98 

in  the  reduction-tube « 90 

on  charcoal 93 

Ferricyanides 80,  168 

Ferrocyanides      79,  167 

Flame,  examination  in 98 

Fluorides      67 

Gold      36 

Group  (acids) : 

First 59 

Second      • 61 

Third 73 

Fourth  84 


192 

PAGE 

Keinsch's  test 25 

Rhodium     174 

Rubidium 176 

Ruthenium 174 

Rutile -...  181 

Selenides 171 

Selenium 174 

Separation  of  acid  sulphides 135 

of  bases :  First  Group 129 

Second  Group 130 

Third  Group 139 

Fourth  Group 146 

Fifth  Group 148 

Sixth  Group , ~~r~v-\    152 

of  basic  sulphides 134 

Silicates 69,  113,  165 

Silicic  acid 69,  165 

Silicofluorides     . 60,  162 

Silver 9 

Sodium 56 

Strontium 51 

Sulphates 59,  162 

Sulphides 81,  168 

of  heavy  metals Ill 

Sulphites 61,  163 

Sulphuric  acid 59,  162 

Sulphurous  acid 61,  163 

Sulphydric  acid 81,  168 

Table  of  group  precipitations 118 

Tantalic  acid 172 

Tantalum 175 

Tartaric  acid 88 

Tartrates 88 

Tellurium 174 

Tests,  preliminary,  in  Dry  "Way 90 

Thallium 174 

Thenard's  blue 42 

Thiosulphites 63 


193 

PAGE 

Thiosulphuric  acid 63 

Thorium 175 

Tin 32 

in  stannic  condition 34 

in  stannous  condition 33 

Titanic  acid 172 

Titaniferous  iron 181 

Titanium 175 

Turnbull's  blue 39,  80 

Uraninite 179 

Uranium      175 

Vanadium 176 

Wolframite     176 

Wulfenite 179 

Yttrium 175 

Zinc 46 

Zircon  .                                                                                                      .  184 


17 


